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Articles from 1998 In April

Genetics: Genetic Considerations In Replacement Females

The objective of regular introductions of new females into the breeding herd is to maximize the amount of lean meat produced/sow/year, and to do it profitably.

The genetic composition, selection criteria and development of the gilt will impact its reproductive ability and longevity. The system through which replacements enter into the herd will influence profit and biosecurity.

Genetic Selection Producers are confronted with the difficult task of selecting replacement gilts from the myriad of available breeds, lines and crosses offered by independent breeders and hybrid swine companies.

Before committing to a genetics program for replacement gilts, producers should analyze their situation. They should first pinpoint the traits needed in their operation that meet their goals before looking for reputable suppliers to select from. Information on suppliers can be collected from other producers and independent sources.

Prior to purchasing breeding animals, evaluate the supplier's genetic improvement program. A sound genetic improvement program should include four points:

1. Accurate, complete performance records;

2. Assessment of genetic merit;

3. Indexes, and

4. Selection of the highest-ranking boars and gilts based on the selection indexes.

The genetic trends for the supplier will show the annual improvements in genetic progress that have occurred.

Because of the sow's integral role in reproduction, representing half the genes in market pigs, focus should usually be placed on several traits by using a selection index.

Maternal line indexes that combine litter size, litter weight, backfat depth and days to market are commonly used.

Also, when making genetic decisions, economically important traits should be emphasized. But it's important to understand the effect that selection has on different traits. Table 1 provides heritability estimates that tell us the strength of inheritance for each trait. Heritability is the percent of the variation in performance that is due to genetic effects. Selection will be less effective for lowly heritable traits, like pigs born alive, because they are affected by environment to a greater extent.

In addition, an estimate of the standard deviation and economic value for each trait is also provided. The standard deviation tells how much variation is present in the population and can be used to estimate where an individual animal ranks in the population.

Economic values indicate how much importance to place on each measure. If two different sources of replacement gilts are expected to differ by .5 pigs born alive, this equates to an expected difference in marginal profit of $6.75. If the females will also produce pigs that are .05 in. leaner when mated to the same terminal sires, there would be an additional economic advantage of $.75 per pig produced. This system can be used to help price gilts based upon their genetic value.

Economic values may vary from farm to farm due to differences in management factors and markets.

Genetic selection of replacement gilts should be balanced with the practical reality of low-selection intensity being placed on commercial replacement females.

If a producer is willing to accept gilts in the upper 75% of a group, then the selection of the leanest, fastest growing, reproductively sound, and structurally correct gilts from maternally selected sows is a valid program.

Visual Evaluation Females that are purchased or retained as replacements should be genetically superior, reproductively sound and structurally correct. Replacement females need to have a thorough visual examination to determine their structural and reproductive fitness. Purchased gilts should also be inspected for mange, lice or other signs of unhealthy conditions before they are allowed to enter the herd.

Feet and legs are important as sows are expected to farrow more than two litters per year, nurse a large litter of pigs for two to three weeks, breed back in seven days or less and live their entire life on solid concrete or wire floors.

An ideal foot on a hog is comparatively large, with both toes the same size. The pastern should be relatively soft (not rigid or erect) and the rear hocks and front knee should be angled so as to not put extreme pressure on the leg joints.

When the animal is walking, the foot should be perfectly flat against the floor and not rotate or turn when the hog takes a step. If the foot rotates or turns on the floor as the animal walks, it sets up a possible sore on the bottom of the foot that can become infected and cause the animal to be in pain and unable to perform. Hogs that have sore inside toes have a tendency to become unsound at an early age. This is due to the uneven balance of weight on the feet and the fact that the foot does not set down on the floor surface evenly.

The overall structure of an animal is the sum total of bone, muscle, fat and skin and how it is assembled to make an animal functional for a specific purpose. The structure of the skeleton is very important because it affects longevity and function. A correct skeleton is one that is shaped in such a way that the hog has ample interior body space for essential organs to function.

In the case of females, a long, wide, deep skeleton allows for more space for reproduction. Correct structure allows a hog to move around on most any surface without difficulty. An incorrect structure will cause a sow to have difficulty getting up and down while she is in the farrowing crate.

The underline of a gilt or sow is extremely important. Replacement gilts must have at least six functional nipples per side and they should be evenly spaced and prominent. The nipples should start far forward on the underline and the underline should be free of pin nipples and inverted nipples.

A pin nipple is any underdeveloped nipple that replaces a functional one. Pin nipples never become functional. An inverted nipple is one where the end of the nipple is held up in the body of the mammary gland and therefore is "inverted." Inverted nipples will sometimes pop out when the sow farrows. But gilts with inverted nipples should generally be eliminated before they are put into the gilt pool because a majority of them will not be functional. Besides underlines, there are other external signs that can be checked for possible reproductive problems.

There are two problems that can be seen in the vulva. The first is a condition where a gilt will show an infantile or extremely small vulva. Infantile vulva is a possible sign of an immature internal reproductive tract.

The second condition is with vulvas that are tipped up on the end. A gilt with a tipped-up vulva may have difficulty getting bred. Gilts with infantile or tipped-up vulvas should not be selected as replacements.

Heterosis Crossbreeding is an important part of commercial swine production systems because of the improvement in efficiency from heterosis and the potential to exploit differences between breeds. A terminal, static cross in which all offspring are market animals takes the greatest advantage of differences in strengths of lines or breeds.

Lines that have superior genetic merit for reproduction should be used to provide the females for a breeding program. Lines that are superior for production traits provide the sires used to produce the terminal market hogs. The pigs marketed then have high genetic potential for production traits and the sow herd has high merit for reproductive traits. Heterosis has the greatest benefit in maternal performance and factors affecting fertility in boars (Table 2).

Ultimately in commercial pork production, selection and crossbreeding combine to achieve the highest level of performance.

An example of heterosis is a cross between lines Y and Z. Let's assume that number of pigs born alive average 10 and 11 for Y and Z, respectively, and that the daughters produced from this cross average 11.5 pigs/litter. The heterosis for number born alive in these YxZ females can be calculated as follows:

Maternal heterosis for number born alive = [(11.5 - ((10 + 11)/2)/ ((10 + 11)/2)] x 100 = 9.5%. Maternal heterosis of 9.5% is equal to the 1 pig/litter advantage the crossbred female has over the average performance of the pure line parents.

In designing and implementing a crossbreeding program, the expected levels of maternal, paternal and individual heterosis are important.

For example, let's compare the F1 female from a YxZ cross to the backcross female Yx(YxZ). The expected heterosis of a cross is determined by the amount of genes the parents have in common. If X and Y are unrelated, that is, they have completely different breed makeup, their offspring will have 100% heterosis.

Therefore, the F1 has 100% heterosis and the backcross has 50% heterosis. In the previous example, the YxZ female had a 1 pig/litter advantage due to heterosis. However, if the YxYZ backcross female were used in the sow herd, this advantage over the purebred lines due to heterosis is reduced to only .5 pigs/litter.

Systems To Produce Replacements Terminal crossbreeding systems offer the best balance of profit per litter and consistencyof production. The terminal crossbreeding system allows the producer to use specialized sire and dam lines and make the most of heterosis. This enables the producer to intensify management, as the genetics of the sows and pigs are consistent.

The problem with terminal crossbreeding programs is obtaining replacement gilts. Gilts can either be purchased or raised on the farm. Purchased replacements can be obtained as weaners or closer to breeding age.

On-farm production can take the form of grandparent (GP), great-grandparent (GGP) or rotaterminal systems and can be structured as a separate herd, contract multiplier or a dedicated portion of the breeding herd.

Producers decide to purchase gilts for many reasons. For small to mid-size production units, purchasing gilts from an outside source is often most practical because within-herd multiplication may not be feasible. This system is the simplest to manage; it maximizes heterosis in market hog production, and allows the genetic decisions and programs to be managed by the supplier. Potential disadvantages can be cost, availability, timing of introductions and increased health risks.

Most producers who raise their own replacement gilts are trying to minimize health risk or reduce total investment in breeding stock.

For within-herd multiplication, a portion of the sow herd (10-15%) is designated to produce replacement gilts for the terminal portion of the herd. These systems lower the potential health risk associated with animal introductions and offer potential cost savings. However, within-herd systems require extra management ability and reduce the number of females devoted to terminal production.

To effectively manage within-herd multiplication, you must be willing to invest extra time, energy and labor into the system. A high level of pig flow management, identification and recordkeeping is required to ensure a consistent supply of quality gilts.

A grandparent multiplier is one of the most commonly used systems to produce replacements. For this system, approximately 15% of the sow herd is made up of purebred or F1 grandparent females and mated to unrelated maternal line boars. Gilts from these matings make up the remainder of the herd (85%) and are mated to unrelated terminal boars with all production going to slaughter. This system can be expanded to a great-grandparent system where 2.5% of the herd are great-grandparents dedicated to producing grandparents, 15% are grandparents producing replacement gilts and 82.5% are used for market hog production.

This system reduces animal introductions and is ideally suited for using AI, but increases management requirements and does not work well in herds less than 600 sows. Grandparent and great-grandparent systems can be formed within herd or established with a multiplier network or user-group. This cooperative approach can be used by smaller producers to maximize genetic improvement and health, while reducing the associated production costs.

Another within-herd system is the rotaterminal. In this system, the sow herd is maintained with a rotational cross of two or more unrelated maternal lines and the top 15% are identified for mating with maternal-line boars to produce replacement gilts. The remaining females and replacements are mated to unrelated terminal boars for market hog production.

In a three-breed rotaterminal, 86% of maternal heterosis can be realized and this is reduced in a two-breed rotaterminal to 67%. This system minimizes animal introductions but requires the greatest level of management.

Tables 3 and 4 compare the market hog production from purchased gilts, grandparent and rotaterminal systems using a four-breed terminal cross.

Maximum heterosis levels are maintained when gilts are purchased, resulting in the most pigs / sow / year. Assuming a profit of $4.00/cwt. and removing differences in breeding animal cost, increased management and lost market hog value, the greatest net return per sow is observed under the grandparent program. These results are only as good as the assumptions in thesimulation (i.e. replacement costs, replacement rates, carcass value program, required management, labor costs.

Another important assumption that was made is that genetic merit is considered to be equal in all three systems. If genetic merit is not equal, the system that offers the greatest genetic potential may have the greatest net return. The program that has the greatest risk of reduced genetic potential is the rotaterminal. Great care must be used to bring in the absolute best maternal boars to produce replacement gilts.

The results of a feasibility analysis conducted by Tom Baas, Iowa State University, are shown in Table 5. Gross margin was compared above all variable fixed costs for F1 grandparent and purchased gilt systems using assumptions for a 600-sow unit. The first column gives the cost to raise or purchase replacement females at 250 lb. The gross profit margin is then shown for different levels of replacement rates and pigs weaned per litter.

These results are somewhat in contrast to Tables 3 and 4, because in the grandparent program we are achieving 100% maternal heterosis through the use of F1s, whereas in the previous examples we were at 85% maternal heterosis by using pure grandparents, so some of the results don't line up exactly.

This table can be used to determine the effect of additional costs that may be incurred in the payment of genetic premiums or royalties, in the evaluation and selection of home-raised replacement females, and to determine the feasibility of various gilt purchase prices compared to the grandparent program. This table also underscores the effect of pigs weaned/litter on profitability by demonstrating the dramatic increase in gross profit margin as pigs weaned/litter improves.

For example, if the replacement rate is 45%, a genetic premium that increases the cost of raising a gilt from $175 to $200/head would decrease gross profit/cwt. from $3.86 to $3.68. A base gross profit margin in a grandparent program of $4.05 corresponds to a cost of raising the gilts of $150/head, along with a market price of $48/cwt., 45% replacement rate and 8.93 pigs weaned/litter. Comparing this base to the purchased gilt program a producer could afford to pay about $220-$225/head for gilts if market price is $48/cwt., replacement rate is 45% and pigs weaned/litter is 9.

The choice of a system for obtaining replacement gilts depends on management ability, herd size, anticipated reproductive performance, cost and availability of breeding stock.

Appropriate age and weight at first mating is very dependent on genotype. Genetically leaner sows will have a larger mature body size than fatter genotypes. Thus, leaner gilts will achieve the same body weight at a younger age than fatter genotypes, but will be physiologically less mature. In many cases, a mating weight of 275 lb.and age of 210 days appears most appropriate for optimum fertility and longevity.

It is also important at first mating that adequate fat stores are available for good lactation and a short weaning-to-estrus interval. This adequate body composition may be represented by a fat depth in excess of .7 in. However, age, fat depth and live weight are not themselves the targets for the right time for first mating but are indicators of age pattern at puberty, the weight pattern of fatty tissue growth, and the relationship between ultimate mature size and the proportion of mature size that is required before reproduction should be initiated.

Maximizing Genetic Potential In order to maximize genetic potential at the commercial level, the nucleus source for breeding herd replacements must be making constant genetic progress. The breeding herd replacements put into commercial production must also be selected according to genetic potential and compatibility (heterosis). When replacement gilts are selected within herd, some objectivity should be used for keep/cull decisions.

To realize genetic potential from an animal, the genotype must be allowed to express itself. This means having access to appropriate feed, water, facilities and absence of disease. Often, the quality of the commercial environment does not allow this full expression.

When making changes or upgrades in the source of breeding animals, an upgrade in management and/or environment may be required for the new, improved genotypes to express their full potential. In order to monitor expression of genetic potential and to make appropriate adjustment to feeding and management programs current, accurate, and useful performance records are required.

How Do I Handle My Gilt Pool?

One of the most frequently asked questions by producers is, "How do I handle the health of my gilt pool?"

Purchased gilts and the much-misunderstood PRRS (Porcine Reproductive and Respiratory Syndrome) have complicated the health stability of the gilt pool.

It seems like a lot of our time as swine veterinarians is spent designing farm-specific isolation, acclimation and gilt pool health programs.

Sadly, many farms don't properly work gilts into the breeding herd.

When PRRS became a serious issue, cutting corners on gilt health, isolation and acclimation started costing in production and consequently profit.

The concept "cool down" had to be dealt with. Allowing time after exposure to on-farm disease, with extra time for gilts to "cool down" and stop shedding, was forgotten. Having time to blood test, vaccinate, provide feedback, and live animal exposure was a new mental and physical facility dilemma.

All of these issues lead to periodic reproductive failure in the existing sow herd. The larger the farms, the longer it takes to reach farm targets.

Unfortunately, many farms didn't return to their previous production levels. They continued to experience a 10% reduction in farrowing rate. Something had to be done to stabilize health of incoming gilts and stop the flood of virus and bacteria pressuring the sow herd's immune status.

Case Study During a routine herd visit, a client said he had six to eight abortions during the last week. This farrow-to-finish, single-site farm was on a weekly farrowing schedule. The producer was doubling his sow herd. A lot of gilts were being introduced to the farm in a short time. Delivery of these gilts always seemed to be late and the producer was in the "I need to breed them right away" mode. A set of gilts were brought directly into the breeding barn the week before.

We suspected PRRS as the cause of the problem. However, to confuse the issue, the farm was also experiencing a swine influenza virus (SIV) break.

The producer chose not to do diagnostic work but preferred to mass vaccinate the sow herd. We chose to use the new killed PRRS vaccine and SIV vaccine. All sows were vaccinated and repeat vaccinated in two to three weeks. The problem quieted down.

The discussion at the next herd visit turned to prevention. What could we do to prevent stressing herd immunity each time gilts were introduced into the breeding herd?

I asked to do a "Swine Genetic Health Survey" on the gilt supply farm. The survey is a two page questionnaire we use to collect health information.

With permission, I contacted the veterinarian of the gilt farm. He was very helpful and up front about the pig health of the multiplier. We found the multiplier was PRRS positive and SIV negative. The blood test results during routine serology told us the gilts were becoming infected with PRRS late in the finisher. By the time the gilts hit my client's breeding barn, they were still shedding a lot of PRRS virus into his sow herd.

Even though his sow herd was serologically (blood test) positive to PRRS virus, some of the pregnant sows didn't have enough immunity to ward off the PRRS virus that the gilts were bringing with them into the sow herd. So some of the sows aborted or ended up as not-in-pig sows.

The question then was how to stop PRRS virus invading this herd. That's where gilt isolation, acclimation and "cool down" became important. We chose to bring three months worth of varying age gilts to the farm at one time. Housing was in outside lots some distance from the rest of the complex. The different age groups were housed in separate pens next to each other. We blood tested them upon arrival and found varying levels of exposure to PRRS with the older gilts showing higher test (ELISA) titers.

All gilts were vaccinated with two doses of killed PRRS vaccine and two doses of SIV vaccine. Recently aborted sows or open gilts (one or two) were placed in each pen, exposing the newly purchased gilts to the farm's PRRS strain. The exposure animals were left in the pens for two weeks.

At that point, we started the "cool down" portion of the system. The breeding gilts became infected and started to shed. Acclimation was really the key post exposure to allow gilts to "cool down" before entry into the sow herd.

The good news is that the farm stabilized and reproduction returned to normal. Increased costs were for vaccine, feed and environment. Decreased cost was out-of-pocket expense for the junior gilts.

Organizing and scheduling gilt deliveries is always the challenge to this system but well worth it. The farm is running well now.

Conclusion Know your own herd health profile as well as the farm where you purchase breeding stock. Remember, their herd health can change just like yours can. Isolation, acclimation and "cool down" are imperative. Time is the key.

Your veterinarian needs to be the important resource person in the development of your farm-specific system.

Sow Efficiency Study

First year start-up data on six genetic lines in the NPPC Maternal line study provides clues about gilt handling, performance differences.

The reproductive life expectancy of replacement gilts has far-reaching, bottom-line effects in today's pork production systems. The purchase of specialized maternal lines represents a significant investment. For producers to realize a sufficient payback, those gilts must be long lived and produce fast-growing, lean market hogs with good meat quality.

The largest study of commercial sow efficiency, including longevity, has completed its first year. Sponsored by the National Pork Board and conducted by the National Pork Producers Council (NPPC), this three-year study is evaluating the reproduction, growth, carcass traits, and meat quality performance of six maternal genetic lines under modern-day commercial management and facilities.

The six genetic lines are being tested for longevity through four parities. Lifetime production of each sow line will be evaluated to determine the economic value of each line.

Testing Protocol A total of 3,560 gilts from 39 different farms were delivered to wean-finish units last spring. The 10-15 day old gilts represented six commercially available genetic lines. Seedstock suppliers participating include: American Diamond Genetics, Danbred USA, DeKalb Swine Breeders (two lines), National Swine Registry and Newsham Hybrids USA. About 590 gilts per line were delivered, grouped 25/pen. Each wean-finish building held about 1,100 pigs.

All gilts were vaccinated for Porcine Reproductive and Respiratory Syndrome (PRRS) and swine influenza virus (SIV) in the wean-finish units. Ivomec was used at entry along with a three-day Naxcel protocol. Mecadox was fed to young pigs according to label directions.

The gilts were fed a 23% protein (1.7% lysine) diet until they weighed 20 lb. From 20-30 lb., a diet with 1.5% lysine was fed. As pigs reached 30 lb. they were switched to a corn-soy starter diet that contained 1.35% lysine and added fat. These diets all contained Mecadox.

>From 70-150 lb., pigs were fed a corn-soy grower diet that contained 1.2% lysine with added fat. Tylan was added to the grower diet at 40 g./ton. The gilt developer diet was corn-soy with .8% lysine. Complete diet formulations are available from NPPC.

All gilts were weighed after 50 days on feed and again at about 165 days of age. Gilt performance in the wean-finish buildings was excellent. Table 1 shows the average gilt performance and a comparison of the best and poorest lines.

The 50-day gains in the wean-finish units compared very favorably with previous research conducted by NPPC using specialized hot nursery buildings. Record analysis verifies the value of heavier pigs at weaning. A 1-lb. heavier pig on delivery translates to a 2-lb. heavier pig at 50 days and 3-lb. heavier at 150 days.

The number of gilts moved to the sow units divided by the number of young gilts placed in the wean-finish buildings is the survival rate listed in Table 1. Gilts weighing less than 7 lb. at entry had a survival rate of 85% while gilts heavier than 7 lb. had a 94% survival rate.

As gilts approached 165 days of age (150 days in the wean-finish unit) they were evaluated for health concerns and abnormalities by the attending veterinarian, the unit manager and an NPPC project manager.

About 3% of the gilts were culled for umbilical hernias, chronic illness and severe injuries. Mortality rate was 5%. The remaining 92% (3,284) of the gilts were given electronic ear tags and moved to two new, 1,600-sow breeding-gestation-lactation units in Iowa. This move occurred when all gilts were 165 days old or younger. No gilts were culled for growth or backfat.

Gilt Prep and Mating Gilts were vaccinated for leptospirosis and parvovirus and housed in gestation stalls. They were ad libitum fed a corn-soy diet with .65% lysine upon arrival to the sow units.

These gilts were exposed to vasectomized boars daily to stimulate estrus. Gilt age at first-observed estrus varied by line. The average was 193 days of age; the best line averaged 178 days, the poorest line, 201 days of age.

The program protocol requires gilts to be mated at the second or later estrous period. Eligible gilts - those exhibiting their second estrus - were mated after they were 205 days old. Gilts were bred when found in estrus and every 24 hours while in estrus. All gilts were artificially inseminated (AI).

Gilts were given three mating periods (60 days) to conceive. Failing that, they were culled. And, any gilt not showing estrus by 300 days of age was culled. All gilts (433) failing these two standards were slaughtered and their reproductive tracts were evaluated by Don Levis, swine reproductive specialist at the University of Nebraska (See Table 2.).

The 108 "normal cycling" gilts in Table 2 included 81 gilts that were found in estrus and bred (some during up to three estrous periods), but never settled, or gilts with their first estrus identified; but subsequent estrous periods were not seen. No gilts were bred on their first estrus. That left only 27 gilts identified in the slaughter checks as"normal cycling" females that were never detected in heat by the farm managers - an excellent result.

Interestingly, 60 of the gilts recorded as displaying estrus actually never cycled, therefore landed in the "not cycling" status when the slaughter checks were complete. Because the program protocol required mating of gilts at second estrus, herdsmen may have reported these gilts in heat if there was any question, thus allowing them to be bred on the next estrus.

The four pregnant gilts listed in Table 2 are victims of unrecorded, weekend matings. By totaling the gilts that were mated, those that cycled normally, those that quit cycling and those found pregnant in the slaughter check, we recorded 89.3% of the gilts entering the sow units as being potentially fertile.

Feeding Feed was restricted to 4 lb./day for the first 14 days after mating, then fed 4.5-5.0 lb./day for the remainder of the gestation period. A lactation diet with 1.2% lysine is fed three times daily to encourage consumption.

After their first parity, sows are fed, ad-lib, from weaning to mating. When bred, all sows are fed 4 lb. daily for 14 days after mating. Thereafter, the amount fed in gestation is based on each sow's weight, lactation weight loss and desired second parity weight gain. Sows are fed to optimize each individual's performance.

Gilt Performance To Date One year after the early weaned gilts arrived at the wean-finish units, 2,679 still remained in the two sow units. That is slightly over three-fourths (75.3%) of the gilts. The best line for survival from early wean entry to one year of age was 86%, the poorest, 70%.

Those 2,679 gilts represent 81.6% of gilts that entered the sow units at 165 days of age. The best line has 93% of the gilts surviving since their move to the sow units, the poorest line has 77%.

The value of early weaned gilts is greatly influenced by the number of gilts surviving, the length of their reproductive life and their reproductive output while in the herd. Likewise, there is a significant investment in developing the gilts and value in acquiring an improved herd health status.

Table 3 shows start-up, first-parity reproduction performance in the farrowing units from December 20, 1997 to March 15, 1998. About two-thirds of the gilts (66%) have farrowed their first litter. On average, the first-litter gilts from the six genetic lines are performing admirably.

In addition to the reproductive performance tracking, backfat loss and weight loss during the first (and subsequent) litters is being recorded. Last rib backfat is measured on all sows as they enter the farrowing crate and within two days after they are weaned. The last rib measurement was chosen because researchers felt it could be measured with more consistency in sows. The Sonic Industries' A-Scan is used.

To date, first-parity gilts have averaged .88 in. last rib backfat going into the crates, ranging from .31 to 1.49 in. The average lactation backfat loss has been .13 in., ranging from zero to .58 in.

Scales strategically located in the alley between the farrowing and breeding-gestation units have made collecting sow weights easy. The average weight of first-parity sows going into the farrowing crates has been 440.5 lb., ranging from 270 to 570 lb. The average weight loss during lactation has been 58.8 lb./sow, but the range was between 2.0 and 140 lb./sow.

Recap The results of Maternal Line Program gilt development project has shed some light on recent trends to early wean gilt purchases. Realizing that information on all first-litter gilts is not in and the results should be treated as "preliminary," these points should be considered:

* Gilt weight on delivery is important. Smaller gilts have a lower survival rate.

* Seedstock supplier history of leg unsoundness and umbilical hernias in gilts. These two factors prevented good gilts from moving into the sow units.

* About 8-10% of gilts moved to the sow units may have reproductive problems that will prevent them from ever conceiving. There appears to be real differences between lines, verified by slaughter checks conducted in this project. Ask for references to check other producers' experience with specific lines. Poor estrous detection could inflate the percentage of gilts blamed with reproductive problems.

* The early weaned gilt value depends on survival rate through breeding.

An extension of this maternal line program is the progeny testing of one pig from each gilt litter. A pig/litter will be randomly selected, then tested for growth, feed efficiency, carcass and meat quality traits. The first group is on test now. Producers will have extensive information to compare the economic values of maternal lines when complete program results are presented in 2000.

This information was compiled and written by Rodney Goodwin, NPPC Director of Production Research, with the assistance of Dave Boyd, NPPC Research Programs Manager. For more information contact Goodwin or Boyd at NPPC, P.O. Box 10383, Des Moines, IA 50306 (515-223-2600).

Gilt Nutrition: Nutritional Programs Enhance Gilt Development

The primary goal of gilt development programs is to prepare gilts to enter the breeding herd at a relatively young age, at a high level of productivity, and to maintain that level throughout a long, reproductive life.

Selecting the most effective gilt development program can be tough because there are many factors affecting reproductive longevity.

Nutrition plays an integral role in the development of gilts. But it can't overcome deficiencies in other parts of the gilt development program. Nutritional advice must be balanced against other management and economic challenges influencing gilt development.

Grow-Finish Period Replacement gilts in the grow-finish phase should receive specifically designed diets. With the widespread use of split-sex feeding, producers have the opportunity to feed these specially formulated diets.

In systems that generate their own replacement females, gilts are commonly selected off the finishing floor at market weight. One drawback to this approach is young gilts are not exposed to a boar to help trigger early puberty.

However, producers can identify and select the fastest-growing, leanest gilts. Those potential replacement gilts should be fed for rapid lean growth right up until they are moved to the gilt pool, much like their terminal littermates destined for market.

If gilts are raised at a site different from the breeding herd, an isolation period should be observed to protect the health of the existing sow herd and acclimate incoming gilts to endemic diseases in the existing herd. Gilts raised in a one-site production system can probably enter their gilt pool directly without an isolation period.

Many producers purchase maternal-line gilts from a seedstock supplier. These gilts may be purchased at a very young age and light weights (50 to 100 lb.) or they may arrive at the farm at or very near breeding age.These gilts were pre-screened before purchase so there is little need to evaluate their lean gain.

Purchased gilts should be moved to isolation facilities upon arrival at the farm. At a young age (140 to 150 days), boar exposure and other management practices should be implemented to encourage an early onset of estrus.

Ideally, specialized management and feeding of replacement gilts can be implemented when gilts enter the isolation facilities or the gilt pool (in one-site production systems) at 140 to 150 days of age. This approach may be ideal for reproductive management, but facility design and pig flow may delay implementation.

Regardless of pig flow or facilities, diets for gilts up to about 200 lb. should be formulated for maximal lean growth and skeletal integrity. Energy and amino acid density of diets for each phase of growth will depend on lean growth potential of the gilt and voluntary feed intake.

The calcium and phosphorus requirements for complete bone integrity are higher than the requirements for optimal growth rate and feed efficiency. Increasing bone mineralization has been shown to increase longevity of sows in some studies, but not all.

Diets for replacement females should be .1% higher in calcium and total phosphorus than diets fed to market gilts beginning at 100 lb. This assumes that diets for market gilts have not been over-fortified. Of course, the actual mineral concentration will depend on voluntary feed intake of the gilts.

Typically, these diets will contain .75% calcium and .65% total phosphorus. This mineral concentration will provide 17 grams of calcium and 14.5 grams of phosphorus intake daily for gilts consuming 5 lb. of feed.

Three Gilt Pool Feeding Strategies The primary goal in the gilt pool is to encourage early expression of pubertal estrus and successfully mate gilts while they continue to grow toward their mature body size. The nature of that body growth as it relates to sow longevity and overall reproductive performance has been the subject of much controversy. Three strategies for managing this body growth have emerged.

Strategy 1 entails full feeding gilts a moderate energy (about 1,500 kcal ME/lb), high protein (16%) diet. The goal is to ensure that the rapid growth of lean tissue, experienced at younger ages, continues right up until the gilt is mated. Increased body tissue reserves of fat and protein provide a nutrient reservoir for gilts to draw on, supporting their lactation and postweaning return to estrus. Some argue that these reserves will enhance longevity of the sow.

Strategy 2 employs restricted feeding (5 to 6 lb./day) of the diet described for Strategy 1 until 10 to 14 days before mating. This strategy allows growth to continue but at a slower rate than if the gilt was full-fed. Moderate restriction of growth rate keeps gilts from getting too fat. But this level of restriction may reduce ovulation rate and size of the first litter.

Therefore, gilts should be full-fed 10 to 14 days before expected mating to increase ovulation rate back to normal levels.

Discontinue this practice of flushing the day after mating because of the threat of increased embryo mortality linked to high feeding levels in the first 10 days after mating.

Strategy 3 involves full feeding a moderate-energy, low- protein (13%) diet to encourage body growth with a high proportion of fat tissue. The goal of this strategy is similar to Strategy 1, except that greater emphasis is placed on the value of fat tissue.

With this strategy, there is a real danger of getting gilts too fat. Excessive condition at mating increases the chance of females being over-conditioned at farrowing. Over-conditioned sows have more locomotor difficulties, farrowing problems and tend to crush more nursing pigs than leaner sows.

Gilt Development Strategies The National Pork Producers Council in cooperation with the University of Nebraska and the University of Tennessee studied development strategies similar to the three feeding regimens described above, looking at gilts from five different genetic lines.

In short, the three groups reported that a higher proportion of gilts assigned to Strategy 2 farrowed their first litter and stayed in the herd long enough to farrow a fourth litter (Table 1).

Significantly fewer females fed for rapid lean gain through 180 days of age (Strategy 1) farrowed their fourth litter, indicating a higher culling rate compared with the other two strategies.

In this experiment, it appeared that feeding to increase fat stores at first mating was neither harmful nor beneficial to sow longevity.

Underlying these three strategies is the central question: What is the most appropriate age, weight and body composition of gilts at first mating?

Work conducted at the University of Minnesota suggested that age, body weight, and body composition at first mating were no different between females that conceived their fourth litter and those females that were culled from the experiment (Table 2).

Similarly, number of pigs weaned over three lactations was not influenced by age or body composition at first mating.

Evidently, age, body weight, and body composition of gilts at first mating are not the most important factors that control sow longevity and lifetime productivity.

Don't ignore feeding and management practices employed during gestation and lactation. Limit feeding during gestation to control weight and fat gain, and maximizing feed intake during lactation to minimize weight loss are key components determining long-term success of the sow herd.

Feed Restriction Advised A moderate restriction in feed intake to slow growth rate of gilts in the late finishing and pre-breeding phases seems to be the most prudent strategy. A target weight of 240-260 lb. at mating on the second estrus is a reasonable target.

Ovulation rate and size of the first litter increases when mating is delayed until the second or third estrus (Figure 1). However, lifetime productivity of third or fourth parity sows was not influenced by delaying mating past the second estrus.

Workers at Michigan State University projected the economic impact of delaying first mating until the second, third or fourth estrus. They found no economic advantage for delaying mating past the second estrus. Delaying mating past the third estrus dramatically decreased returns per hundredweight of pork produced. Facilities, production flow and effectiveness of the gilt pool will dictate the appropriate estrus period for first mating. In most systems, gilts will be mated at second or third estrus. Mating at the first estrus or after the third estrus is not recommended.

In many instances, with fast-growing pigs, moderate feed restriction in late finishing and pre-breeding will be necessary to prevent gilts from getting too heavy and fat.

However, the specific approach may vary from farm to farm depending on genetics and management practices. Restricting feed intake to 5.0-5.5 lb./gilt/day of a diet that contains about 1465 kcal metabolizable energy (ME)/lb. and .8% total lysine will provide 7.3-8.0 Mcal of ME and 18-20 grams of lysine daily. This level of restriction should allow continued growth of body tissues without excessive fattening while having little or no negative effects on age at puberty.

In some production systems, restricting feed intake is not feasible. Use of low- energy feed ingredients that dilute the energy content of the diet may be a reasonable alternative but can be difficult to implement effectively in some systems.

Breeder Vitamins, Minerals Vitamin needs of the reproducing female are greater than those of the terminal animal. For gilts entering the breeding herd, the typical vitamin premix in the finishing diet should be replaced with a "breeder" vitamin premix. This premix should contain elevated levels of the fat-soluble vitamins A, D, E and K, and the water-soluble vitamins with special attention to choline, biotin and folic acid that are relatively low or absent in typical finishing diets.

Likewise, mineral requirements of breeding swine are elevated relative to market animals. Calcium and total phosphorus concentrations of diets should be .9% and .8%, respectively. Concentration of other minerals are also increased in breeder premixes.

Switch to higher levels of vitamins and minerals typical of a sow diet when gilts are moved into the isolation facilities.

The following recommendations can be used as guidelines for the development of gilts from 50 lb. through first mating.

1. House gilts to allow feeding of specially formulated gilt development diets. 2. Feed for rapid lean gain until gilts weigh about 200 lb. 3. Beginning at 100 lb., increase dietary calcium and phosphorus concentration .1% above typical grow-finish diets for improved skeletal development. 4. Initiate boar exposure at about 150 days of age (200 lb.) if possible, to encourage early expression of puberty. 5. Feed diets in the isolation facilities and gilt pool that contain the same vitamin and mineral fortifications as diets for the sow herd. 6. Restrict feed intake in the gilt pool to 5.0-5.5 lb./gilt/day of a corn-soybean meal diet that contains .8% lysine. The primary goal is to slow growth by restricting energy intake. 7. Full-feed gilts 10-14 days before mating on second estrus to achieve increased ovulation rates associated with flushing. 8. Reduce feed intake back to pre-flushing levels immediately after mating to reduce embryo mortality.

Pork Forum '98: NewVoluntaryCheckoff Explored

Pork Forum delegates discuss building non-checkoff monies.

Pork producers may face the option of a new voluntary pork checkoff in the future. This voluntary checkoff would be used to fund areas that cannot be financed by the current, mandatory Pork Act checkoff. Fighting legal battles, responding to trade disputes and lobbying for fair environmental regulations cannot be paid for from Pork Act checkoff money.

So producer delegates of the National Pork Producers Council (NPPC) approved preliminary plans for a voluntary checkoff. The delegates met at the NPPC annual meeting held during the Pork Industry Forum in Reno, NV, March 5-7.

NPPC delegates will take the proposed checkoff back to states for discussion and guidance. They plan to meet again this fall to act on the checkoff proposal.

The proposed checkoff, also called a "voluntary investment program," would raise much-needed money for handling issues outside of the Pork Act. The Pork Act states the current checkoff of 45 cents/$100 value of market hog can only be used for producer education, pork promotion and research.

New NPPC President Donna Reifschneider presented the proposed voluntary investment plan to the delegates. She reported state pork producer groups cited a growing need for non-checkoff money.

"During a Federation Council meeting, we did a survey on the non-checkoff needs in states," Reifschneider said. "Of the 42 states, 36 said non-checkoff needs were increasing dramatically. The most common state increase was 25% annually.

"The leading cause for increases are state and local regulations, legal aid expenses, lobbying and staff time related to these interests," she added.

Current Non-Checkoff Budgets Until now, non-checkoff money was raised by membership fees, trade shows and allied industry contributions on the state level. Together, the states generate about $3 million each year in non-checkoff money, according to Reifschneider.

NPPC generates about $2.6 million annually from World Pork Expo, allied industry contributions and the Packer Processor Industry Council (PPIC). They also receive other money from such sources as Pork Report and state producer groups. The NPPC budget in 1998 calls for $3.2 million to be spent in non-checkoff areas.

However, the need is much greater than the current revenues, according to Reifschneider. NPPC expects to need $1.25 million/year more in non-checkoff dollars for the next three years. Plus, state producer groups estimate their needs to grow $2 million/year for the next three years in addition to their current non-checkoff revenue.

The outside sources for non-checkoff funds may be at the limit. "The pool of money out there is shrinking and we were looking at ways to generate our own funds," Reifschneider said. "We hear from producers that it is harder to get involved in the state fairs and those kinds of things. And the states' annual meetings have fewer companies to be involved in their conventions."

The proposed investment checkoff could help solve the fund-raising problems.

Voluntary Checkoff The proposed investment program calls for a 5 cents/market hog or sow checkoff at the point of animal sale. The money raised would be split 50% to states and 50% to NPPC.

The PPIC will be strongly urged to establish a contribution, too, at 2.5 cents/animal. These funds would be allocated by NPPC where needed.

If approved, producers will need to sign up for the voluntary checkoff.

"We've talked to packers about this (checkoff)," Reifschneider explained. "It will be treated as a line item deduction. There would be a form for the producer to fill out saying (the market) may take out the contribution. It would be a one-time signing. If you change your mind, it can certainly be rescinded."

Reifschneider said they anticipate 70% participation for the proposed investment checkoff. This amounts to about $3.4 million annually.

The proposal facing the NPPC delegates calls for the NPPC Board of Directors to evaluate the need for the non-checkoff funds each year.

The NPPC delegates approved the voluntary concept and agreed to meet at a special session before Oct. 1 to act on the proposal.

Delegate Discussion During the annual meeting, NPPC delegates generally supported the proposal. In fact, North Carolina already has a state checkoff with funds allocated to producer needs not covered by the Pork Act checkoff.

Jim Stocker of Murphy Family Farms and an NPPC board member, said Murphy Family Farms currently contributes 3 cents/pig to this fund.

"It has worked in North Carolina and can be made to work (nationally)," he said. "I certainly speak in favor of establishing something that will take care of the big need we have. It seems to be growing faster than our hog business."

Delegates Against Local Rules After some debate, delegates to the NPPC annual meeting approved a resolution discouraging local government jurisdiction in environmental rules.

Instead, the delegates supported federal and/or state jurisdiction of environmental rules for agriculture. This move is a desire to head off hundreds of different rules being considered by local governments including county commissions and health boards.

Sometimes the rules devised at local levels are based on emotion and not sound science. This can affect the viability of pork production in those areas.

The delegate support of this resolution followed earlier action on a set of national environmental standard regulations. During 1997, representatives of NPPC negotiated with federal and state environmental agencies. Together, these groups developed standard environmental rules for hog farms.

Called the National Environmental Dialogue on Pork Production, the standard rules were released in December 1997. (See story in National Hog Farmer, Jan. 15, 1998, page 8.) Delegates gave their stamp of approval to the dialogue during the NPPC annual meeting.

The pork industry is the first livestock industry to work with environmental groups on developing model regulatory guidelines for hog farms of all sizes. The guidelines are based on proven science and generally accepted best management practices.

It is hoped the dialogue will be used by state and federal groups for formulating environmental rules. This will create consistent, reasonable rules.

The dialogue covers such items as: permitting procedures; design and management standards; siting; developing nutrient management plans; training and certification for manure handling; inspections; and emergency responses.

Other Resolutions The 150 NPPC delegates considered 21 resolutions during the annual meeting. They approved 11 resolutions.

Food Safety The issue of food safety and a pork producer's responsibility was the focus of three resolutions.

The delegate body approved one proposal urging packers to require Pork Quality Assurance (PQA) Level III certification by Jan. 1, 2000. The resolution also urged NPPC to continue to educate producers about the PQA program.

Also approved was a resolution supporting further work on a national identification system for all market hogs, sows and boars. The identification system would allow traceback to the producer in the event of animal health or residue problems.

Trichinae, PRRS Trichinae and PRRS (Porcine Reproductive and Respiratory Syndrome) were the subjects of two other resolutions approved by the NPPC delegates.

One resolution called for the pork industry to aggressively pursue steps to certify U.S. pork products trichinae-free. The resolution also called for communicating this to domestic and international pork markets.

While the U.S. supply of pork is virtually trichinae-free, no inspection system exists to certify this. As the U.S. strives to increase pork exports, the need to prove the trichinae-free status becomes more important. Countries like Denmark have tested every hog for trichinae for several decades with no positive tests. This diligence has helped make Denmark successful in pork exports.

Action taken on another resolution supported a research project to study the feasibility of eliminating PRRS infection in U.S. herds through on-farm management practices.

The resolution called for summarizing current PRRS research. Management recommendations must be developed for controlling or eliminating PRRS. And finally, the resolution called for the dissemination of effective, on-farm protocols for managing the disease.

Emergency Health Plan Following a presentation on the recent hog cholera outbreak in The Netherlands, NPPC delegates asked for the development of a national animal health emergency management plan.

The approved resolution called for NPPC to work with state associations, state animal health officials, USDA and other commodity groups to develop this plan.

Recent outbreaks like hog cholera and Foot-And-Mouth Disease in Taiwan highlight the devastation these diseases can bring to a hog industry. The U.S. is not immune from such disease outbreaks and should be prepared.

The emergency plan should include things like:

* Appropriate level of inspection of passengers at U.S. points of entry.

* Ability to conduct surveillance programs.

* A swift, aggressive response system.

* A regionalization plan to minimize the impact of the disease in the U.S.

* Procedures for providing indemnification to affected herds.

Pork And Beans An Iowa resolution asking for lean pork to be included in the popular pork and beans canned product was amended and passed.

Delegates decided to work with packers, processors and food manufacturers to improve and add more value to family favorites like pork and beans.

The delegates also approved a resolution pushing for more aggressive marketing of the "Pork. The Other White Meat" campaign.

Producers not paying the required checkoff on farm-to-farm feeder pig and breeding stock sales have a grace period to begin paying without penalty. The National Pork Board voted to halt penalties until July 1, 1998, to allow producers to begin remitting the checkoff.

Board President Esther VerMeer stated some producers may not have realized their responsibility to pay the checkoff on farm-to-farm sales of weaner or SEW pigs and breeding stock. During the grace period, the penalty of $1,000/infraction and 1.5%/month late fee will be waived.

The mandatory pork checkoff produced $61 million in 1997, up from $58 million in 1996. The National Pork Board offered their report at the recent Pork Industry Forum.

The National Pork Board is responsible for the collection and disbursement of the pork checkoff. They reported revenues were much higher last year than expected. The year ended with a record surplus of $10.9 million.

However, in 1998, the board expects lower revenues due to lower hog prices. They are estimating a $56 million budget.

National Pork Board delegates chose eight nominees for possible selection to the 15-member Pork Board. Five seats for three-year terms are vacant on the board. The eight names will be submitted to U.S. Secretary of Agriculture Dan Glickman. Glickman will then appoint five members to the National Pork Board.

The nominees in order of delegate body priority are: Greg Boerboom, Marshall, MN, and Bobby Bryan, Dillwyn, VA, (both incumbents); Tom Floy, Thornton, IA; Donald Berend, Wichita Falls, TX; Kaye Whitehead, Muncie, IN; Nash Johnson, Clinton, NC; Richard Alig, Okarche, OK; and Mike Lewis, Tulare, CA.

Details of a program to seek and test odor control technology was announced at the Pork Industry Forum. The National Pork Producers Council (NPPC) plans to spend $3.5 million for an Odor Solutions Initiative. The initiative was first announced last summer at World Pork Expo.

The Odor Solutions Initiative will identify and evaluate biological, chemical, mechanical and management technologies to reduce odor. The initiative also will reward the individuals bringing this technology forward.

Beginning in April, a selection committee will solicit entries from individuals and private industry for products to be tested. Each product will be tested on three to five farms per technology. The testing is scheduled to begin in July.

Odor and water quality will be monitored at the farm sites while the technology is in place. Odor will be measured by olfactometry, chemical analysis and any other documented method.

A third-party verification of odor measurement and laboratory procedures will be provided by a private firm specializing in these procedures.

The intent of the initiative is to see how well these technologies or products live up to their claims, reports John Kellogg, Yorkville, IL. Results of the testing will be provided to producers at the end of the program.

Kellogg adds NPPC needs producers willing to have the technology tested on their farms.

With little fanfare, the National Pork Producers Council (NPPC) elected the first woman president in its history. Donna Reifschneider of Smithton, IL, took over the position during the Pork Industry Forum held recently in Reno, NV. Reifschneider succeeded Jerry King, of Victoria, IL.

Reifschneider and her husband Jim own a 600-sow, farrow-to-wean operation. The couple also raise corn, soybeans, milo and wheat.

In the coming year, Reifschneider vowed to focus NPPC's efforts in two areas acutely affecting producers: the environment and hog prices. She cited the on-farm environmental audit and odor assessments along with a new program, the odor initiative, as ways to help producers solve environmental problems.

"We hope in the next few years to have a majority of hog farms involved in the assessments," she said. "We're trying to make our producers better stewards and actually better producers in the process.

"Price is the other area on producers' minds," she said. "We at NPPC know this is a serious challenge. We are working in the retail area, getting the Other White Meat tale out and showing retailers the value of pork products."

Reifschneider also said they will continue to push for more government purchases of pork.

While a member of the NPPC Board of Directors, Reifschneider served as chair of the Demand Enhancement Committee, Food Safety Committee and Budget Committee. She also chaired the Pork Quality Assurance Committee and participated in the National Environmental Dialogue on Pork Production.

Officers Elected The new NPPC president-elect is John McNutt of Iowa City, IA. McNutt is part owner and general manager of his family's 300-sow, farrow-to-finish operation. He also assists his wife, Ilene Lande, in the operation of her biological products company.

Craig Jarolimek of Forest River, ND, was named NPPC vice president. Jarolimek and his wife Dawn operate a 5,000-head finishing operation. They also raise wheat, barley and sugar beets.

Other Election Results NPPC Board of Directors - Elected to three-year terms: Jarolimek; Lynn Green, Morgan, MN; Max Waldo, DeWitt, NE; and Jill Appell, Altona, IL.

Randy Buller, Apple Valley, MN, was elected to the associate member seat on the NPPC Board of Directors representing allied industry. This is a two-year term. He is district manager for Elanco Animal Health.Pork Industry Nominati ng Committee - Elected to the committee responsible for selecting, interviewing and recommending candidates for national leadership positions were: Rick Rehmeier, Augusta, MO; Charlie Miller, Alexander, NY; and Don Buhl, Tyler, MN.

A Nickel For Your Thoughts

In the spirit of the town hosting the recent Pork Industry Forum, delegates to the National Pork Producers Council laid some cards on the table.

The site was Reno, NV. The "dealer's choice" (a.k.a. delegates' choice) game in town - how to generate the non-checkoff dollars needed to lobby for fair environmental regulations, import-export balance, fight legal and legislative battles. It's a high stakes game.

How high? A specially formed, NPPC non-checkoff working group told delegates that member states currently generate about $3 million annually while NPPC adds $2.6 million to the unrestricted funds till. The committee projected they will need an additional $3.25 million/year for the next three years to provide the state and national lobbying and legislative support needed.

It's not news that the pork industry is being challenged on many fronts. Environmental, regulatory mandates will be drafted in the next few years that will affect how you raise hogs, regardless of herd size.

Your delegates at the annual meeting were pretty sure you'd want to be at the table when the next hands are dealt.

But they wrestled with a resolution calling for a new, supplemental checkoff over and above the mandatory checkoff provided for in the Pork Promotion, Research and Consumer Information Act of 1985. This resolution called for a voluntary contribution of a nickel per hog or sow marketed. They dubbed it the "voluntary investment program" or VIP.

VIP. Has a nice ring.

Good idea.

Bad timing.

Asking for more money when the market's in a slump does not constitute an opportune moment. But the urgency justified the risk of asking.

Delegates approved the concept but delayed taking final action until they could bounce the idea off their constituents.

So, consider yourself dealt into this high stakes game. The face cards you'll receive are the too-familiar issues of the day - environmental, regulatory, odor control, legal, legislative. And, there's a wild card - the VIP card supporting the voluntary nickel checkoff.

Will you play it?

Will you ante-up a nickel per hog or sow in an effort to win the big pot? Or, are you satisfied to let the chips fall where they may?

What's really at stake here?

* Precedent-setting court cases are being sent to court dockets daily. The win-loss record will affect how you raise hogs in the future. A fund is needed to defend your interests.

* Environmental concerns will not go away anytime soon. Lobbying with good science to represent producer interests is needed for reasonable guidelines to be drafted.

* Food safety issues, import-export markets, animal health and drug issues, and more.

The NPPC's non-checkoff working group's report predicted that if the voluntary program was initiated, about 70% of the hogs would be checked off.

I support the voluntary investment program. But I'm going to propose a little twist. I think we should shoot for 100% participation for a specified period of time. Five years seems reasonable. Plug in a "sunset clause" for the nickel program. That's a reasonable, short-term commitment that would provide a well-financed, focused representation of pork producer positioning.

Under the VIP plan, half of the monies are returned to the states where the real battles are won and lost. You might even call for a 60-40 split. Dealer's choice. You're the dealer.

Do I see some grimaces in Des Moines? Many might argue that the need will not end in 2003. New issues will replace the old.

They're probably right. Still, I favor a five-year performance review for several reasons.

First, it strengthens the argument for full participation or at least minimizes the number of producers who will rescind their consent for the checkoff when asked. Give the program a window of opportunity to work.

Second, unless producers agree the program should be extended five years from now, it has an endpoint. If it's a resounding success, it won't be hard to sell in 2003.

Finally, full endorsement of the voluntary program signals to all of agriculture, business, government and the general public a sense of solidarity and commitment. It says you mean business.

In some respects, this new call for a voluntary checkoff is reminiscent of my first year of reporting in this industry. The checkoff was a nickel/head; it was voluntary; and, there was a consistent, impassioned plea for greater participation. Then, as now, producers were reminded of the need for more money to tackle greater challenges - production of leaner pork and boosting pork consumption.

Years passed. Goals and visions grew. The checkoff was bumped to a dime.

Eventually, a national referendum provided for a mandatory checkoff and the monies needed to do the work of providing research and consumer information, pork promotion for all. But, the restrictions of the Pork Act and the challenging legislative and regulatory issues today are testing the metal of modern-day producers.

In many ways, the need for nickels in 1998 may be greater than it was in the '70s. Are you as committed to the pork industry as your parents and grandparents were when they first signed on to the voluntary nickel checkoff?

Overview: Options for Maintaining An Effective Gilt Pool

Breeding herd reproductive efficiency starts with the gilt pool. The gilt pool is defined as a group of young females selected as potential replacements for the breeding herd.

The term "gilt pool" doesn't refer to a location or facility. Rather, it refers to a group of females available to be bred and added to the breeding herd as needed.

In today's modern farrowing operations, there are a fixed number of farrowing crates per group. An efficient breeding herd manager will strive to keep those farrowing crates full to maximize throughput and maintain pig flow throughout the system.

As breeding herd females are regularly culled for infertility, unsoundness, age, etc., replacement gilts from the gilt pool are needed to complete each farrowing group. Proper use of the gilt pool will ensure that a pregnant female is available to fill each farrowing crate according to a planned schedule. The breeding system and farrowing schedule will determine the number of gilts required in the gilt pool.

Choice of Crossbreeding System The crossbreeding system that maximizes profit for commercial producers in most cases is a terminal crossbreeding system. A terminal cross in which all offspring are marketed offers several advantages over other breeding schemes:

1. Heterosis is maximized;

2. Greater product consistency is possible;

3. It's easier to implement and manage;

4. It allows the best use of genetically selected sire and dam lines. Lines with superior genetic merit for reproductive traits provide females for the crossbreeding system. And specialized lines that excel in growth and carcass traits are used as terminal sires.

Terminal crossbreeding systems have become the industry standard for most operations for several reasons.

First, larger and more specialized pork production units have developed specific mating schemes to make within-herd gilt replacement more feasible.

Second, independent seedstock suppliers and companies have expanded their herds to meet the market for replacement gilts and/or grandparent females.

High herd health practices have made the regular purchase/introduction of these females more practical.

Finally, the use of artificial insemination (AI) and advanced genetic evaluation techniques have made highly selected terminal and maternal sires more readily available.

Optimum Breeding System The purpose of a breeding system is to make the most profit from the operation. The breeding system can be defined as the design and type of crossbreeding program and the breeding stock used in it.

To obtain the most profit, the breeding system has to produce a consistent, high-quality product as efficiently as possible, given a fixed level of inputs (facilities, capital, labor, etc.).

The best breeding system won't always provide the greatest production potential or the least capital cost. It will generate an appropriate number of pigs over time, resulting in "optimum" pig flow, not necessarily maximum pig flow.

Assuming the terminal crossbreeding system is used, a key question is how to obtain replacement females. Whether to purchase all replacement females or establish a within-herd scheme for producing the needed replacements will depend on each producer's situation.

Raising Gilts For Gilt Pool Several requirements should be met before a producer sets up a within-herd gilt multiplication system. First, and foremost, you must be willing to put forth the extra management required. Extra discipline, time and effort are essential. These systems require identification of all nucleus females, an evaluation and selection program to ensure the best sow herd candidates are selected, and, management of the production supply.

Before you decide to raise your own replacements, analyze the potential benefits and the costs associated with the extra effort.

In a within-herd multiplication system, a portion of the sow herd is designated to produce replacement gilts for the terminal portion of the herd. Advantages include lowering the herd health risks involved with introducing new animals into the herd plus a potential cost savings. However, you must be committed to the extra management required and recognize that you are reducing the number of females devoted to terminal market hog production. Several examples of within-herd multiplication of replacement females will be discussed.

Within-Herd Multiplier A within-herd grandparent multiplier is one of the most common systems used. (See example in Figure 1.) Close to 15% of the sow herd is made up of purchased F1 grandparent females (ie.: Hampshire x Landrace) that are mated to unrelated maternal line boars or inseminated using purchased semen. Gilts from these matings are used to maintain the other 85% of the sow herd, mated to unrelated terminal boars with all offspring going to market.

Great Grandparent Plan Another example - an extension of the grandparent system - is the within-herd great-grandparent program. It includes another level where great-grandparent females are used to produce the grandparent females within the herd.

For example, the Hampshire boars and Landrace females would be the great-grandparents in the previous example. Approximately 2.5% of the total sow herd would be devoted to producing these F1 grandparent replacements, while 15% would be used for parent female production, and 82.5% would be used for terminal market hog production. This system reduces the number of outside females that must be purchased and is ideally suited for AI.

However, this program requires even greater management ability and attention to detail, and reduces even further the number of females available for terminal market hog production. It also does not work well in herds under 400-500 sows.

Rotaterminal System A third option to consider is the rotaterminal system in which replacement gilts are produced by approximately 15% of the sow herd which is maintained in a rotational cross of two or more unrelated maternal lines. These gilts are then mated to unrelated terminal boars for terminal production. This system has an advantage in that startup females are purchased only once. It is, however, even more complex to manage since it is critical that rotaterminal females are mated to the correct breed or line of boar in order to maintain maternal heterosis.

In a three-breed rotaterminal, 86% of potential maternal heterosis is realized if the correct rotation of breeds is maintained. If two breeds are used, potential maternal heterosis is reduced to only 67%.

The percentages of the herd needed to raise replacement gilts that are included in these three options are rule-of-thumb estimates. Actual number of females needed will depend on production levels, sow herd culling rate and selection intensity. Breeds shown are examples to maximize both maternal and pig heterosis in each system. Various other breed or line combinations are also available.

Multiplier Options Another popular way to obtain replacement gilts is through a network multiplier or a user-group multiplier. In these systems, a group of producers set up a separate venture to produce replacement breeding stock for the user group. One of the previously described mating schemes is used and the group is generally tied directly to a seedstock supplier. Each member purchases shares (stock or sows) in the user group that fits with their production schemes.

These network multipliers are designed to maximize genetic improvement, health (biosecurity) and reduce costs and management to maintain grandparent or great-grandparent females. Startup costs will probably be greater, but this system has the potential to reduce genetic costs and provide long-term genetic gain.

Regardless of the system used, development of potential replacements starts at birth. A record of specific matings to produce replacement females must be maintained; gilts in those litters must be identified at birth by earnotching and/or eartags.

Some producers choose to raise these potential replacements with their contemporaries, while others may pen them separately for identification and selection. This also allows them to be fed separately and developed on a different plane of nutrition.

Buying Gilts Purchasing all gilts from an outside seedstock source has become popular for numerous reasons. Given a terminal crossbreeding system, it is the simplest system to manage since no breeding decisions have to be made. All terminal boars (or semen) can be mated to any female in the herd. Buying all gilts makes the most of terminal production in the herd. These should be the most profitable pigs to produce since market hogs produced in these terminal mating systems are generally leaner and more efficient than the barrows and cull gilts produced in the maternal-line litters.

If all replacements are purchased, a producer will depend on his seedstock supplier to do his "genetic work" for him. As a result, the genetic merit of the commercial producer's herd will directly relate to the genetic progress made in the seedstock supplier's herd.

Potential disadvantages of buying all replacement females are the initial cost, limited availability, timing of introductions into the herd and the herd health risks involved.

Cost and availability questions are primary considerations. A consistent, reliable supply of gilts is essential when all replacements are bought.

Frequent introductions of breeding age females aren't feasible for herds that have initiated segregated early weaning (SEW), multiple-site systems to improve herd health. Some seedstock suppliers have introduced SEW gilt (<21 days of age) and junior gilt (40-50 lb.) programs to meet the demands of these herds.

Under these programs, gilts are placed in an isolation facility separate from the base herd. Introduction at an early age allows more time for females to be isolated, monitored for disease status, and acclimated to the health status of the base herd.

An acclimation period following isolation allows new gilts to build immunities comparable to the base herd. Normally this is accomplished by introducing a few sentinel animals into the isolation facility after the initial monitoring period. These sentinel animals may not have clinical symptoms of diseases present in the base herd, but differences in immune systems may cause the new gilts to exhibit an immune response upon exposure to the disease pathogens. An adequate acclimation period will facilitate close monitoring of any immune response and allow time to establish a common health status between the new gilts and the base herd.

It should be noted that introducing females at or near market weight (5-6 months of age) increases the temptation to reduce the time spent in isolation and acclimation. The isolation and acclimation periods should be a minimum of 30 days each to allow adequate time for disease monitoring and adjustment to the breeding herd environment. Proper time spent here will boost lifetime reproductive performance and longevity.

Genetic Merit It is important to consider the relative genetic merit of purchased vs. home-raised gilts. Remember that the genetic merit of home-raised gilts in a grandparent system is a function of the genetic merit of the grandparent females and the maternal sires to which they were mated. Gilt selection efforts will contribute very little to the genetic improvement of the herd and are relatively unimportant when compared to the importance of the genetic merit of the grandparents.

Because of the small number of grandparent females needed and the premium generally paid for them, it is very important that they have performance records and are selected from the top end of a herd making consistent genetic improvement.

In addition, AI has become a powerful tool in making the best maternal sires in the industry available to commercial pork producers for replacement gilt production.

Perhaps of even greater importance is the genetic merit of purchased replacement gilts. If these gilts come directly from a multiplier herd that is supplied by a nucleus herd making significant genetic improvement, this improvement will be channeled directly to the commercial herd and genetic lag will be minimized.

But if the multiplier herd is using average or below average females from a nucleus herd, genetic progress in the commercial herd will be limited. It is equally important to select both boars and gilts from herds that have a sound testing and selection program.

Number In Gilt Pool A planned breeding and farrowing schedule, along with previous production records, will help determine how many gilts are needed in the gilt pool. Season of the year, age, environment and genetics are factors that may affect the number of females exhibiting estrus and their conception rates.

Naturally, the number of replacement gilts needed to keep each farrowing group full must be determined in advance. Culling rates and previous conception rates for gilts and the existing sow herd will determine how many gilts should be bred. In general, at least three gilts should be selected for the gilt pool for each farrowing crate to be filled. Even more gilts are needed during problem breeding periods or if pen breeding is used.

It is generally recommended that females are not bred before they reach 7-711/42 months of age. This will ensure that gilts are on at least their third heat period before being bred. This usually results in an increase in ovulation rate and fewer rebreeding and lactation failure problems than if gilts are bred at their first or second estrus. Temporary situations may make it advantageous to breed females earlier than their third heat cycle, but lifetime production will likely suffer.

Cost Comparisons Accurate cost comparisons between the various systems should be made to assess the most cost-effective for each herd. Each system may have a different genetic cost based on structure of the breeding herd, initial purchase price, replacement rate, expected production levels and economic values specific for the herd.

Remember that the value of different alternatives varies from farm to farm and the lowest genetic cost may not be the best. The genetic merit of the pigs produced must also be weighed in evaluating the benefits of the various systems.

Gilt Nutrition Energy intake of developing gilts can be restricted after 180-200 lb. without delaying puberty. This can be accomplished by hand feeding 5-6 lb. per day of a 14-15% protein, well-balanced diet. This program will allow moderate lean tissue growth and save on feed costs over ad libitum feeding. It also allows accumulation of adequate fat reserves necessary to support reproduction without increasing unneeded body weight that may decrease longevity and contribute to unsoundness during development or later in the sow herd.

Summary Effective management of the gilt pool can greatly affect the reproductive performance of the breeding herd. Choice of a system for obtaining gilt pool replacements depends on management ability, herd size, expected reproductive performance and availability and cost of breeding stock replacements. All must be considered when weighing the merits of each system.

The purchase of replacement females for terminal crossbreeding systems is an alternative that should be given careful consideration. If a consistent supply of genetically superior females is available from a reliable supplier, a high level of productivity in an easy-to-manage system can result. Properly designed terminal crossbreeding programs will achieve a maximum level of both maternal and pig heterosis.

Purchasing all replacement females must also be regarded relative to the cost and the potential disease risk involved.

Home-raised females in a grandparent system can be cost effective and greatly reduce the disease risk involved in the continuous introduction of replacement gilts.

AI is well suited to within-herd multiplication systems and is especially helpful in small herds to overcome inefficient boar use with natural matings in grandparent systems. It also allows the use of superior maternal boars that might not be available through natural service.

Herd Health: Health Considerations When Introducing Gilts

There are several ways to introduce new genetic material into a breeding herd. Live animals may be purchased or produced within a system as selects, breeder weaners or weaned pigs.

Or, new genes may enter a herd via semen, embryos or cesarean-derived piglets. Regardless, the goal of any introduction is to improve genetics while maintaining herd health.

Creating Stability Properly managing replacement gilts forges a key link in providing homogenicity (equality) of health between incoming stock and the existing sow herd.

This homogenicity and stabilization of immunity is very critical in maintaining a balanced, sustainable production system.

To reach this goal, any animals received should go through a period of isolation, acclimation and recovery prior to being introduced into the new herd. Producers should establish a similar system for both internally and externally sourced animals. When designed and operated properly, a gilt development program should lower the cost of producing weaned pigs.

Isolation Period Isolation is defined as segregation from the main herd. It is a period of time to observe pigs for any health changes and conduct any desired profiling which may include observation of clinical signs, serology, necropsies and sentinel animal assessment.

This period also allows the genetic supplier to contact you if there has been any health change in the source herd. This health change information is available through monthly veterinary visits, production data and routine diagnostics.

Isolation has the function of protecting the receiving herd from exposure to known clinical diseases and allowing identification of incubating diseases at time of delivery. It also prevents disease challenges in the recipient herd from overwhelming incoming animals until they are prepared

Isolation should occur 21-30 days post-delivery and be completed in a separate facility from the main herd.

Ideally, this separation should be a half mile or more from the breeding herd. However, many producers have found it is consistently effective to separate incoming animals by 75 ft. from the breeding/gestation population.

The herd health risk is a function of agent, separation distance, animal population, age of the pig, biosecurity and physical location of the isolation unit with respect to the sow population. As the size of the group in isolation increases, and separation distance decreases, the risk of aerosol disease transfer increases.

The isolation unit is typically similar to a standard finishing facility but many designs are used effectively. These standard buildings are often totally slotted, natural or power ventilated, double curtain with a shallow pit. The pit should be self-contained for waste storage to coincide with the period of isolation. The buildings are sized according to the flow of animals into and out of the facility and the length of the isolation period.

Installation of a crate in every other fenceline is a very practical means of housing cull animals for natural exposure. These crates also serve as boar housing for estrus stimulation and detection.

The people flow assumes that animals in isolation are of high risk to the main herd. The building should have a separate shower and entry. Ideally, one person has the responsibility of caring for these animals. People within the main unit can manage the isolation unit as long as it is visited as the last task of the day and the personnel maintain separate boots and clothes and shower in or out.

The isolation facility must be all-in, all-out in order to maintain a period of isolation. It cannot be operated continuous flow.

Acclimation Period Acclimation is the process of incoming animals becoming accustomed to new facilities, recipient herd pathogen levels and endemic disease agents in the receiving herd.

Acclimation involves vaccination of animals to develop acquired immunity, and exposure to receiving herd pathogens to develop natural immunity. The purpose of acclimation is to stimulate individual animal and population immunity.

Achieving homogenicity or equality of immunity within a very large percentage of the population is crucial to reducing subpopulations within the herd.

Acclimation starts after isolation is complete. The time required for this stage is directly related to success of natural exposure, time required for immunity to develop to vaccine and natural exposure and the recovery period to reduce risk of disease spread.

The acclimation program should be herd and system specific, based on the health status of the incoming animals and the receiving herd.

Because of this variability, a system of disease profiling should be used to identify if natural or vaccine exposure has been successful in controlling agents such as Porcine Reproductive and Respiratory Syndrome (PRRS), parvovirus, etc., that can be readily analyzed. Placement of negative sentinels into the acclimated population with subsequent testing either with serology or necropsies can also be used in this assessment.

In short, the program for a single herd will be different than the program for multiple sow herds commingling weaned pigs. The program should be reviewed semi-annually or if a health change occurs in the sow herds.

Acclimation should occur as a controlled challenge, because some populations can be overwhelmed, resulting in disease and death in pigs.

To develop a specific program, you need to have a solid understanding of the health status of your own herd.

The vaccination program will depend on your herd health strategy. One-site, farrow-to-finish herds may have a minor vaccination program, while segregated-production herds will have a vaccination strategy to maximize protective colostral antibodies for the piglets. The latter will depend on an intensive vaccination program to stabilize health, avoid sub-populations and allow successful, segregated production.

Timing of vaccination depends on the vaccine used and time of exposure. Vaccination may begin late in the isolation period to stimulate immunity prior to natural exposure. Vaccination and/or exposure to the more common agents such as Mycoplasmal pneumonia and swine influenza virus (SIV) is a critical factor in maintaining sow herd stabilization (immunity) to prevent spread through segregated nursing pigs.

A word of caution: Let your veterinarian direct the acclimation program as there are times such as pseudorabies elimination when acclimation doesn't apply.

Natural acclimation entails contact with "seeder" animals from the recipient herd along with feedback. Exposure assumes that the seeder animals from the receiving herd are actually shedding viruses or bacteria. Cull sows often serve as the contact animals, but may be a poor source of seeders for some diseases.

Good candidates are low-parity sows, non-breeding gilts or gilts that have aborted or been rebred. Low-parity animals are the best candidates because they have just been exposed to the pathogen load within the sow herd. Those young gilts/sows haven't produced solid immunity that would reduce their ability to transmit disease organisms.

Unfortunately, our ability to identify these successful candidate animals is limited.

A more common source of seeders for PRRS is nursery pigs. Nursery pigs have longer viral activity, increasing the odds of successful exposure early in the acclimation period.

Serological profiling for agents like PRRS can identify the exact group for exposure and can tell if successful exposure has occurred.

Contact animals are introduced to the incoming group for two to four weeks and then are removed. The length of exposure depends on the disease agent and the transmissibility between the two groups. Sampling either by serology, polymerase chain reaction (PCR) or virus isolation may help identify candidates as seeders.

The key is identifying the group that has recently been actively infected because they have a much higher risk of shedding. As a guide, one cull, parity-zero gilt or parity-one female to 20 animals has been satisfactory for exposure. The exact ratio of exposure population to incoming population is also unscientific and depends on the disease agent.

With some disease agents, such as transmissible gastroenteritis (TGE), one clinically affected animal is effective. In other cases, several animals must be used to increase the chance of exposure and the rapidity of exposure.

It's vital that these seeder animals be dispersed throughout the acclimation population. This can be done either by housing them within all the populations or by moving them daily between the various groups. Seeder pigs or pens should be rotated once or twice daily during the early acclimation period to increase exposure.

Naive groups being acclimated will generally transmit the agents readily amongst themselves, but slow transmission increases the length of the acclimation period or the number of contact animals needed. This contact should be completed aggressively the first few days of the acclimation phase.

Acclimation is also frequently done by oral feedback of mummies, viscera (lungs and intestines) of stillborns, weak newborns from recently farrowed litters and feces of recently farrowed sows. The exact feedback protocol is also unscientific but the general guidelines are:

* Collect viscera from one stillborn and one newborn, weak pig per 10 head of gilts to be fed back. Use stillborns and weak pigs from as many litters as possible, with no more than four pigs from any one litter.

* Collect all the mummies in one day.

* Collect 11/42 cup of manure per gilt to be fed back.

* Collect parts of five placentas per 20 animals. Collect the day of farrowing.

Once this material is collected, homogenize it using a grinder or garbage disposal. Mix with equal parts of cold water. Scatter this material into troughs, at least two cups per gilt, twice for two weeks. Or, more frequent feedback is useful as long as it is done appropriately. Assign someone to this task and make them accountable.

Most recently, acclimation has focused on PRRS. But this procedure is also extremely valuable for parvovirus, enterovirus, SIV, mycoplasma, rotavirus and E. coli.

Historically, producers have realized the benefit of acclimation because it controls viruses causing reproductive losses.

Recovery The last phase of health management for incoming animals is recovery. This period begins after isolation and acclimation. The recovery period allows stabilization of individual and group immunity, reducing risk of disease spread to the receiving sow herd.

It is commonly accepted that a recovery of 60 days or longer is necessary for the entire group to be at low risk of transmission, before adding them to the existing herd. The importance of this recovery period has been seen with PRRS. Most animals stopped shedding PRRS virus 21-30 days post-exposure.

Certain incoming groups may need a recovery time of 90 days or longer to limit transmission risk. Profiling for PRRS can give you guidelines as to the stability of the immunity and the length of recovery time.

The exciting point here is that recovery time from PRRS seems to work for other agents including parvovirus, SIV and the enteroviruses.

To provide a 60-day recovery period, design the isolation, acclimation and recovery (I/A/R) process to have the animals available for servicing. If your target breeding age is 210 days, and you need at least a 60-day I/A/R period, replacement animals need to be received at 140-150 days of age.

If you have just one gilt developer facility, you can't receive animals at less than nine-week intervals to avoid continuous flow. In this situation, you will need to receive staggered-age gilts in a batch program.

More practically, two or more gilt developer units are required. This allows you to alternate the flow between the two units. Each gilt developer unit needs to be designed based on the inventory of animals, length of occupation and exit age and weight of the gilts. Maintaining a separate period of isolation followed by acclimation and recovery works out to a period of delivery through introduction into the breeding herd of 90 days.

Gilt developer models and operational processes need to be discussed in depth with your veterinarian. Figures 1-4 illustrate various models.

The combined health management program covering I/A/R may make it more practical to receive staggered age and weight gilts as breeder/weaners or weaned pigs.

Breeder/weaners are typically 50-60 lb. If you do not receive or enter them at staggered ages and weights, you need multiple isolation or developer buildings.

Accepting younger pigs allows for a longer period of exposure and monitoring to improve the success of the acclimation.

It also provides an extended recovery time for those groups of animals requiring it, while still keeping the flow of gilts available to meet weekly service targets.

Receiving weaned pigs or breeder/ weaners makes several groups available to the production system and provides breeding flexibility in case of problems.

The same processes/procedures must be followed for animals in an internal, closed-herd multiplier as from an outside source. Don't assume herd health of those sources is similar to that of your herd. Profiling has proven that internally produced replacement animals aren't consistently healthy. They need to go through the same acclimation and recovery period as externally produced replacements.

Groups will vary from PRRS negative to PRRS positive within the same building or system, especially if there is room separation or building separation of groups.

In a successful, segregated production system (two-site, three-site, multi-site) the segregated groups will have a different health status than the sow groups.

Boars should be brought in using the same system as gilts unless they are going to a separate, off-farm stud.

Table 2 illustrates a timeline for a typical gilt development system.

There are costs in constructing and operating gilt developer facilities for successful I/A/R. The data in Table 1 was derived from implementing gilt development plans in a commercial system.

Summary The benefits of properly conducted I/A/R have been identified by numerous researchers. The gilt developer system needs to incorporate all aspects of this program. The design and sizing of these facilities depends on the capacity for the gilt pool within the breeding herd facility, the age and weight of service, the age and weight of the incoming animals and the length of I/A/R.

Success depends on following detailed procedures and designating a person accountable for implementation.

Isolation - a population that is separated from other pigs for a period of time.

Acclimation - the process of becoming accustomed to a new level of health and farm conditions.

Quarantine - a period of detention or isolation of incoming animals from the receiving herd with restrictions placed on entrance to, and exit from, any facility where a communicable disease may exist.

Gilt Housing: Building Design Can Affect Reproduction

The successful development of replacement gilts requires the integration of several factors including health, nutrition, genetics, housing and management practices.

The facilities these potential sow herd replacements are housed in must meet several criteria:

* Enhance estrous stimulation;

* Maximize the percentage of gilts cycling at an appropriate age;

* Maximize the percentage of gilts showing regular estrous cycles;

* Optimize soundness of feet and legs;

* Optimize body condition and backfat;

* Prevent gilts from infecting the existing sow herd at time of entry;

* Enhance adequate exposure of gilts to farm microorganisms before breeding;

* Optimize the utilization of labor and,

* Optimize construction cost of facilities.

Because of the Porcine Reproductive and Respiratory Syndrome (PRRS) virus, numerous management practices and building schemes have been set up to manage the gilt pool to control PRRS virus shedding in the breeding herd.

Common Design Questions Regardless of the production system used to rear gilts (Figure 1), pork producers most often ask the following questions:

* Floor space - Although the minimum floor space needed to prevent a delay in reaching puberty has not been established, the floor space required at various weights is listed in Table 1. These space provisions should allow young gilts to mature properly.

* Gilts per pen - Scientists at the U.S. Meat Animal Research Center allotted gilts at 4.5 to 5 months of age to groups of 3, 9, 17 or 27 gilts/pen. The gilts were kept indoors and given 11.6 sq. ft./gilt. Gilts were fed daily 3.5 to 4 lb. of a 13% protein diet after 5 months of age.

Daily estrous checks (10 min./pen) with a mature boar were initiated when the oldest gilt reached 7 months of age and continued until the youngest gilt reached 9 months of age.

Gilts in pens of three had 12% to 16% fewer regular estrous cycles than gilts in pens of 9, 17 or 27 (Figure 2). There was no difference in the percentage of gilts showing regular estrous cycles as the number of gilts/pen increased from 9 to 27.

* Synchronization of estrus - Cycling gilts should remain in their pen and not be removed. Australian research found the synchrony of puberty in response to boar contact was significantly better when pubertal gilts remained in their pens for 5-15 days after exhibiting either first or second estrous periods, than when they were removed at the first sign of puberty. The differences were measured in terms of days to puberty and age at puberty. Boar exposure started when the gilts were 160 days of age.

* Photoperiod - The influence of photoperiod on age of puberty and proportion of gilts reaching puberty remains controversial.

Many scientific studies evaluating the effect of photoperiod on attainment of puberty used boar exposure to detect estrus; consequently, the true effect of photoperiod can't be determined.

Table 2 shows the proportion of gilts reaching puberty was greatest when gilts were exposed to mature boars, regardless of whether duration of daylight is increasing or decreasing. Neither the type of lighting (fluorescent or incandescent) nor intensity of light (lux) significantly influences puberty attainment or ovulation rate in gilts.

Moreover, it is most economical to maintain developing gilts under cool, white fluorescent light (270-500 lux at eye level of gilt) for 10 to 12 hours/day. Complete darkness delays puberty as compared to 11 hours/day of natural light.

* Ambient temperature - Elevated ambient temperatures have detrimental effects on puberty in gilts.

When the University of Missouri allotted crossbred gilts at 140 days of age to either a chronic heat stress (92 degrees F, 35% relative humidity, 12 hours light: 12 hours dark) or "optimal" environment (60 degrees F, 35% relative humidity, 12 hours light: 12 hours dark), more gilts reached puberty by 230 days of age under optimal conditions (90%) than under heat-stress conditions (20%). Average age at puberty was not statistically different (optimal, 204 days; heat-stress, 213 days).

The number of eggs ovulated at puberty were numerically greater in optimal conditions (12.1) than in heat-stress conditions (9.3).

All gilts not reaching puberty by 230 days of age, on both treatment regimes, received 1,000 IU of pregnant mare serum gonadotrophin (PMSG).

Gilts that were heat-stressed had a greater incidence of cystic follicles than those housed in optimal conditions (50% vs. 0%). Feed intake and average daily gain on a pen basis were not different between heat-stress and optimal conditions.

The effect of heat stress on behavioral estrus, ovulation rate and length of estrous cycle in post-pubertal gilts is controversial. In view of this controversy, it is advisable to protect replacement gilts from high environmental temperature (>85 degrees F) by providing adequate shelter and supplemental cooling to prevent severe stress.

The proportion of gilts cycling during the summer months is less than other times of the year (Table 3).

Therefore, the need to have more gilts for breeding during summer months can cause housing problems. To help increase the proportion of gilts cycling during the summer months, be sure to provide boar exposure.

* Air quality - The rearing of gilts indoors and exposing them to a gaseous environment may cause delayed puberty.

Purdue University found that 33% of gilts reared in an environment having 5-10 ppm ammonia reached puberty by 203 days of age, compared to 12% for gilts reared in an environment containing 20-35 ppm ammonia.

However, the proportion of gilts attaining puberty by 240 days of age was similar, as was their average age at puberty.

A study at the University of Nebraska evaluated the effect of a "dirty" environment (20 ppm ammonia gas concentration) versus a "clean" environment (< 10 ppm ammonia gas). The proportion of gilts showing first estrus by 240 days of age was 96.7% in the clean environment and 92.9% in the dirty environment. The dirty environment tended to delay age at puberty (200.5 vs. 192.8 days).

* Housing of boars - The exposure of prepubertal gilts to a mature, sexually aggressive boar will greatly reduce the age of the gilt at first puberty.

However, stock people need to be sure estrous gilts are not "refractory" to boar stimuli at the time of estrous detection. Gilts in estrus show a rigid and immobile response when they receive boar stimuli (sound and smell), but after a few minutes they need to relax their muscles (Table 4). Relaxation can start to occur at five to 10 minutes after receiving boar stimuli (the refractory stage). Once relaxed, it is much more difficult to detect estrus. Thus, to maximize the efficiency of detecting gilts in estrus, boars should be housed away from gilts to ensure gilts do not receive continuous boar stimuli prior to estrous detection.

* Housing gilts with sows - Although boar exposure is generally more effective to stimulate puberty in gilts than mature sow exposure, research shows that contact (continuous or 20 minutes/day) with mature sows can stimulate and synchronize the onset of puberty in gilts.

An Australian study evaluated the effect of exposing crossbred gilts (starting at 159 days of age) for 20 minutes/day to either an estrous gilt, estrous sow, anestrous gilt or anestrous sow on puberty attainment. The sexual status of the exposure female had no effect on the proportion of gilts reaching puberty.

However, the proportion of gilts reaching puberty was greater for gilts exposed to sows than those exposed to non-farm-raised gilts (Figure 3).

A similar study in Australia found that the percentage of gilts attaining puberty within 55 days of the puberty-inducing stimuli was greater for gilts exposed to estrous sows (80%) than anestrous sows (40%).

Research has not been conducted to determine whether the combination of boar and estrous sow exposure have an additive effect on puberty attainment.

* Estrous stimulation. To maximize the boar effect on stimulating puberty in gilts, a mature boar (10-11 months of age) with a high level of sexual behavior (mounting, chomping, nosing, chanting), should be placed in a pen of gilts two or three times daily. Attainment of puberty is 14 to 30 days quicker when gilts are exposed at 160 days of age to boars with a high degree of sexual behavior compared to low sexual behavior boars.

* Estrous detection - The facility in which gilts are provided boar exposure should be designed for easy movement of people and animals. Provide quick and easy-to-use latches, gates that cut off alleys when open and non-slick floor surface of alleys.

Research at the University of Nebraska found that the rate of estrous detection was not different when gilts are heat checked in stalls (67%) or pens (68%) with fenceline boar exposure. However, the rate of heat detection (fenceline boar exposure) was higher when gilts in pens were moved to the boar room (81%) than in gilts where heat detection occurred in their stall or pen.

Also, the immobilization response occurred more rapidly in gilts relocated to the boar room (1.7 min.) for heat detection than gilts heat checked in their stall (2.5 min.) or pen (2.0 min.). The University of Nebraska evaluated the accuracy of estrous detection of cycling gilts in response to either physical or fenceline contact with a boar in the boar room.

On the first day of estrus, 100% of the gilts receiving fenceline boar exposure were detected in estrus during the first five minutes, compared to 83.8% of gilts receiving physical boar exposure. But, within 15 minutes, 100% of the gilts receiving physical boar exposure were detected in estrus. And, interestingly, in gilts detected in heat with physical boar exposure, estrus was expressed about .6 days longer than gilts in which heat was detected with fenceline boar exposure.

* Maintaining estrous cyclicity - Australian research has suggested that boar contact is required during the post-pubertal period to maintain normal estrous cycles in gilts. The proportion of gilts found cycling over three cycles was 97% for gilts receiving daily boar exposure versus 66% for gilts not exposed to boars.

* Gilt housing - Replacement gilt facilities need to be designed so cycling and acclimating gilts can be easily exposed to mature boars. The facility in Figure 4, specifically designed for replacement gilts, provides numerous advantages. All gilts entering this facility must first go through an isolation protocol.

* One end houses acclimating gilts and gilts eligible for mating, the other end houses bred gilts in stalls. Boars and mating pens are placed between the two sections. When artificial insemination is used, old, sexually aggressive boars are housed in the boar room. Eligible gilts are moved into the boar room which contains a high level of boar stimuli. When in the boar room, gilts can receive either fenceline or physical boar contact.

Acclimating gilts are provided boar stimulation to induce puberty by either taking a boar to their pen or moving the gilts to the boar room. Boars can be easily taken to the bred gilt section to check for recycling. Because the boar room is totally enclosed, the proper ambient temperature for natural service boars can be maintained year around.