National Hog Farmer is part of the Informa Markets Division of Informa PLC

This site is operated by a business or businesses owned by Informa PLC and all copyright resides with them. Informa PLC's registered office is 5 Howick Place, London SW1P 1WG. Registered in England and Wales. Number 8860726.


Articles from 2004 In April

Specialized Feeding of Sows, Gilts

As production systems begin to implement parity-based segregation of the breeding herd, producers and nutritionists have been able to take advantage of greater specialization of feeding programs for gilts and sows.

It's not that we haven't been aware of the differences in nutrient requirements of gilts vs. sows. But in facilities where they are housed together, it becomes extremely difficult to implement two separate feeding programs.

Because gestating gilts are still growing and depositing greater amounts of protein during gestation than sows, and typically have lower lactation feed intake, our nutritional programs have focused on meeting the gilts' requirements, realizing that in many instances we are overfeeding sows.

Therefore, parity-based segregation should allow for more specialized nutritional programs to minimize the costs of overfeeding, and hopefully, enhance breeding herd performance.

Gilt Development

The most important thing to remember in designing and implementing a gilt development protocol is that the feeding program will be of secondary importance to items such as early boar exposure and estrous detection, genetics and selection criteria, and environmental and other management factors.

That's why it is possible for many different types of feeding programs to be successful, depending on how the other important management criteria are implemented.

For instance, if replacement gilts are farrowed on the farm, or delivered as early weaned pigs, they can be fed the same nursery diets as the commercial pigs. In some cases, it may be desirable to slightly increase the feed budget to allow more of the early starter diet to be fed. This provides added insurance against any potential replacement gilts falling behind or becoming stunted.

A good time to do a preliminary selection is when gilts leave the nursery, examining them for good structural correctness, having at least 12 teats and the absence of ruptures or hernias.

Research from the University of Alberta and the Prairie Swine Centre in Saskatchewan, Canada, suggests that growth rate of replacement gilts should be neither too slow, nor too fast. Those researchers suggest that the ideal weight at breeding should be approximately 300 lb. Gilts that grow too slowly wind up being held too long before they reach their ideal breeding weight, thus accumulating excessive non-productive days.

For example, if a gilt weighs 200 lb. at first estrus, she will be on her fourth or fifth estrus by the time she reaches the 300-lb. target weight. Gilts that grow too fast have a large mature size and run the risk of increased susceptibility for locomotion problems that may affect lifetime breeding performance.

Table 1. Diet Options for Developing Gilts from 50 lb. to 250 lb.
Three phase Three phase with Fat
50 90 150 50 90 150
Ingredient 90 150 250 90 150 250
Corn 68.80 74.35 87.15 68.80 74.35 79.75
Soybean meal, 46.5% 28.25 22.80 10.10 28.25 22.80 12.40
Choice white grease 5.00
Monocalcium P, 21% P1 1.20 1.13 1.05 1.20 1.13 1.15
Limestone 19 18 18 19 18 17
Salt .35 .35 .35 .35 .35 .35
Vitamin premix with phytase .15 .15 .15 .15 .15 .15
Trace mineral premix .15 .15 .15 .15 .15 .15
Lysine HCl .15 .15 .15 .15 .15 .15
TOTAL 100.00 100.00 100.00 100.00 100.00 100.00
Desired Lysine, % 1.15 1.00 0.65 1.15 1.00 0.70
ME2, kcal/lb 1,504 1,506 1,510 1,500 1,505 1,611
Protein, % 19.0 16.9 12.1 19.0 16.9 12.5
Calcium, % 0.70 0.65 0.60 0.70 0.65 0.60
Phosphorus, % 0.64 0.60 0.53 0.64 0.60 0.55
Available phosphorus, % 0.32 0.30 0.27 0.32 0.30 0.29
Available phosphorus equiv., % 0.40 0.38 0.35 0.40 0.38 0.37
Lysine:calorie ratio, g/mcal 3.47 3.01 1.95 3.48 3.01 1.97
Avail. P:calorie ratio g/mcal 1.21 1.14 1.05 1.22 1.15 1.04
Feed budget, lb./pig 90 165 350 90 165 315
2Metabolizable Energy

Therefore, from 50 lb. to breeding, replacement gilts should be fed diets that promote good growth rate and skeletal development. These diets can be very similar to rations fed market hogs, with the exception that they won't be formulated for maximum growth and leanness, and they will contain greater levels of calcium and available phosphorus for bone strength.

Genetic potential for lean growth may be a factor in selecting lysine and energy concentrations of these gilt developer diets. With extremely lean genotypes, it may be advisable to add fat to the last developer diet (combined with relatively low lysine) in order to increase second-parity (P2) backfat depth to about 16 mm (.63 in.) by the time of breeding.

Other, less-extreme genotypes may achieve this 300-lb. target weight and 16 mm, second-parity backfat depth at breeding on regular grain and soybean meal-based diets formulated to lysine levels slightly below standards for maximum growth rate and leanness.

The justification for the weight and P2 backfat depth targets of 300 lb. and 16 mm at breeding are based on the premise that gilts need to have enough total body protein reserves to buffer against excessive weight (protein) loss during lactation, when feed intake is generally low.

Recent data from the University of Alberta indicates that milk production (litter weaning weights) and subsequent reproductive performance were greater in high-lean body mass sows that lost less protein in lactation. They speculate that a larger lean mass may buffer against the decreases in performance associated with severe protein loss during lactation. There is probably less conclusive evidence to support the recommendation of 16 mm of P2 backfat depth at breeding, other than this amount will allow for easily reaching the targeted fat depth of 19 mm (.74 in.) at farrowing, based on expected gestation feed intake and weight gain.

The diets listed in Table 1 are possible options for moderate growth during the development period. Care should be taken to closely gauge gilt weight gain, so if the targeted weight is not reached or exceeded, diets can be modified based on specific rearing conditions.

In most cases, at around 250 lb., gilts will be moved to the breeding barn, where feed intake should be limited to approximately 4.5 lb./day, again adjusted based on the goal of a 300-lb. gilt at 210 days of age.

Then around Day 190 — or two weeks before breeding — feed intake should be increased to 6 lb./day to flush gilts and increase ovulation.

Immediately after breeding, feed intake should be cut back to 4 lb./day for five to seven days postbreeding.

Then, once sows have been bred, feed intake can be adjusted based on size and desired weight and backfat gain during gestation.

The data in Table 2 shows the calculated amount of extra feed above maintenance (approximately 4 lb./ day) provided over the first 100 days of gestation to achieve the desired weight gain.

Table 2. Feed Intake Above Maintenance Requirements to Achieve a Certain Weight Gain*
Desired weight gain Total feed, lb. Extra feed required from Day 0 to 100, lb.
30 45 0.2
40 60 0.3
50 75 0.4
60 90 0.5
70 105 0.7
80 121 0.8
90 136 0.9
100 151 1.1
*Maintenance requirements for a 300-lb., 350-lb. and 400-lb. gilt will be met with 3.25, 3.50, and 3.75 lb./day of a corn-soybean meal diet, respectively. These intake amounts assume all sows will be fed 6 lb./day from Day 100 to 114.


Management of the replacement gilt has become a critical issue in determining the overall reproductive efficiency of the breeding herd. A management and nutrition program that allows for moderate levels of growth performance from birth to selection will positively affect reproductive performance and longevity.

It is apparent that gilts should enter the breeding herd with greater tissue reserves (protein), and should be fed without significantly reducing these reserves, to ensure a long breeding life.

Parity Effects on Lactation Feed Intake

Parity 1 (P1) and P2 females consume less feed than older parities (Table 3).

If only one diet is practical on the farm, parity distribution should be evaluated to determine the most economical approach. This will typically mean formulating diets to meet the gilts' requirements, realizing we will be overfeeding the rest of the herd.

However, if production systems have the opportunity to separate gilts and Parity 1 sows from older sows, consider using the following approach:

Formulate the first diet for P1 and P2 females (this diet should be formulated to minimize protein tissue loss), and formulate the second diet for the other parities (this diet should be formulated to maximize litter weight gain in the older parities).

Table 3. Lactation Feed Intake and Lysine Intake as Influenced by Parity and Dietary Lysine Level
Item 1 2 3 4 5 6 7
Lactation feed intake, lb. 10.1 11.5 13.5 13.1 14.0 13.7 14.3
Lysine intake with one diet (.95% lysine), g./day 43.7 49.6 58.1 56.4 60.3 59.0 61.8
Lysine intake with two diets (.9% and 1.2% lysine), g./day 55.2 62.6 55.1 53.5 57.2 55.9 58.5
Adapted from Dritz et al., 1994.

This approach will allow similar total amino acid intakes for all parities as demonstrated in Table 3. Thus, formulating their diet to a higher amino acid level allows similar grams per day of consumption.

But use caution. The data in Table 3 was collected from a farm with excellent lactation feed intake with about 140 lb., 21-day adjusted litter weaning weights. On many farms, lactation feed intake may be lower; therefore, the dietary lysine percentages may need to be adjusted accordingly.

Farm Diet Options

The diets listed in Table 4 are possible options for producers with parity-segregated breeding farms.

Gestation and lactation diets are formulated to offer gilts slightly higher lysine and other amino acid concentrations compared with sows. Some producers may choose to add soy hulls or another source of fiber to their lactation diets.

In these cases, the dietary lysine percentage has been changed to correspond with the decreased energy content of the diet, and the anticipated increase in feed intake to provide similar caloric intakes.

Table 4. Gilt and Sow Gestation and Lactation Diet Options
Gestation diets Lactation diets
Ingredient,% Gilt Sow Gilt Sow Gilts Sows
Corn 81.70 83.50 78.35 80.01 58.60 65.80
Soybean meal, 46.5% CP2 14.50 12.70 12.95 11.25 34.70 27.45
Choice white grease 3.00 3.00
Monocalcium P, 21% P1 1.65 1.65 1.55 1.55 1.55 1.55
Limestone 1.00 1.00 1.00 1.00 1.00 1.01
Salt .50 .50 .50 .50 .50 .50
Vitamin premix with phytase .25 .25 .25 .25 .25 .25
Trace mineral premix .15 .15 .15 .15 .15 .15
Sow add pack .25 .25 .25 .25 .25 .25
Soy hulls 5.00 5.00
TOTAL 100.00 100.00 100.00 100.00 100.00 100.00
Total lysine, % 0.65 0.60 0.63 0.58 1.20 1.00
ME, kcal/lb 1,490 1,490 1,441 1,442 1,550 1,550
Protein, % 13.7 13.0 13.2 12.6 21.1 18.4
Calcium, % 0.76 0.75 0.76 0.76 0.80 0.80
Phosphorus, % 0.68 0.67 0.64 0.64 0.73 0.70
Available phosphorus equiv., % 0.48 0.48 0.46 0.46 0.48 0.48
Lysine:calorie ratio, g./mcal 1.98 1.83 1.98 1.83 3.51 2.93
Avail P:calorie ratio g./mcal 1.47 1.46 1.45 1.44 1.42 1.39
2Crude Protein

Estimating Gestation and Lactation Feed Intake

With the help of closeout spreadsheets, there is so much more accurate information today on nursery and growing-finishing pig feed intake than in the past.

Yet in the sow herd, we seldom evaluate herd gestation feed intake, and in lactation, many still rely on inaccurate and outdated feed intake cards.

Better estimates of gestation and lactation feed intake can be estimated based on monthly feed delivery.

To calculate average herd gestation feed intake, simply divide the tons of gestation feed delivered over a set time period by the number of gestation crates, times the number of days in the period.

In situations where sows are group housed or combinations of gestation crates and pens are used, divide feed delivery by gestating sow inventory, times the number of days in the period.

Total Feed = 625 tons × 2,000 lb. = 5.27 lb./day

Crates × Days 650 crates × 365 days

Using this method of calculation, we target a gestation feed intake of between 5.0 and 5.4 lb. as ideal. When feed intake amounts are higher than this, a representative sample of the herd should be scanned for backfat, because average backfat will very likely exceed the desired 19 mm (.74 in.) at farrowing.

In lactation, we take the average of two calculations. The first divides the total feed delivered in a set time period by the number of farrowing crates, times the number of days in the period.

Total Feed = 419 tons × 2,000 lb. = 10.2 lb./day

Crates × Days 450 crates × 182 days

The second method is based on the number of lactating days. From computerized sow records, we determine the number of litters weaned in a period, times the average lactation length; then the total feed delivered is divided by this number.

Total Feed = 419 tons × 2,000 lb. = 12.2 lb./day

Litters × Lactation Length 3,615 × 19 days

The first method should underestimate average lactation feed intake, because it counts the days that crates are either empty or containing sows before they farrow as consuming lactation feed. The second number overestimates lactation feed intake, because the feed given to sows before they farrow is counted as lactation feed.

However, the true daily lactation feed intake has to be somewhere between 10.2 lb. and 12.2 lb., or an average of about 11.2 lb.

If there is greater than a 3-lb. difference in the estimated feed intake among the two equations, this usually indicates that sows are gestated for several days in the farrowing crates and further analysis is needed.

Converting Manure to Oil

A University of Illinois (U of I) research project that converts swine manure to crude oil could be a surprising key to reduced crude oil imports and could possibly create a new industry in the U.S.

U of I agricultural engineer Yuanhui Zwang has refined a thermochemical conversion (TCC) process to make it more efficient and faster.

“If 50% of swine farms adopted this technology, we could see a $1.5 billion reduction in crude oil imports every year,” he projects. “And swine producers could see a 10% increase in their income, about $10-15 per hog.”

Other pluses are that minerals are preserved in the after-treatment stream, odor is reduced and the oxygen demand of manure is reduced by 70%.

Using a batch reactor, researchers achieved an average of 70% conversion from swine manure volatile solids to oil. At that conversion rate, the manure excreted by one hog during the production cycle could produce up to 21 gal. of crude oil. A farm raising 10,000 market hogs/year could produce 5,000 barrels of crude oil/year.

Zhang is further refining the conversion process and hopes to develop a pilot plant to analyze the oil properties and seek alternative applications of the TCC oil.

Options For Parity Segregation

The evolution of swine production system design has been a rapid, dynamic process in the last 40 years. The progression from batch farrowing outdoors to continuous-flow, confined production to three-site production and finally, to multi-site production has led to significant improvements in productivity and cost reductions.

Producers have come to recognize that even with multi-site production, there are still improvements that could be realized. They also recognize that gilts are a unique population of animals in the breeding herd that are often overlooked when it comes to meeting their special needs.

In addition, young breeding animals are often the source of disease for the entire production system. This fact has been reinforced to the swine industry with the emergence of the porcine reproductive and respiratory syndrome (PRRS) virus.

To address these challenges, a group of producers in Canada, led by swine veterinarian Camille Moore, began experimenting with the concept of maintaining gilts on separate farms and rearing the offspring separately.

Thus, parity segregation was born. Since that time, there have been a number of additional production systems in both Canada and the U.S. that have implemented parity segregation systems.

This article describes the authors' experiences working in and with these systems, and the potential benefits and real-world challenges of operating a parity segregation system.

Benefits of Parity Segregation Systems

Parity segregation has numerous benefits for both sow and growing pig production. As noted, gilts (also known as Parity 0 or P0 females) are the source of active disease transmission for the sow herd, creating active disease in both gilts and Parity 2 and greater (P2+) sows. The sow herd has lower mean performance and reduced predictability of weaned pig output over time due to both chronic disease and periodic epizootics from new disease introductions.

By separating out gilts, which tend to have higher rates of disease transmission than mature sows, the rate of infection in, and the risk of new disease introductions to, the majority of the sow population are reduced.

Gilts, by mechanisms that are not entirely understood, tend to clear most diseases during their first gestation. Multiple studies in Sweden, for example, have documented that Mycoplasmal pneumonia can be eliminated from sow herds by not introducing females under 14 months of age to the sow farm.

The production benefits of separating gilts are consistent and substantial. The biggest production benefit to gilt separation is the specialization of labor in breeding, feeding and caring for them. This specialization allows the customization of mating patterns and feeding practices from the first service through farrowing. If P1 females are retained for breeding on the gilt farm, then this specialization of labor can be continued though the P1 service.

As a practical matter, gilts on traditional farms are often overlooked for their special needs. The separation of the gilt farm makes implementation of gilt management practices easier, because there is only one location in a system to require implementation. In larger systems, staff can be dedicated full-time to these responsibilities, thus increasing the chance that the goals of the gilt management program are achieved.

Less expensive diets are an additional benefit. The gilt's daily amino acid requirements are higher than P2+ sows. Traditional mixed-parity farms feed diets that meet the gilt's needs. The feed costs can be reduced by feeding lower-cost (lower amino acid) diets to Parity 2+ gestating and lactating sows.

Furthermore, segregating the offspring of P2+ sows has shown substantial improvement in growing pig performance, primarily attributed to improved health. Moore, addressing the annual meeting of the American Association of Swine Veterinarians, reported on improvements in average daily gain, feed conversion ratio and a reduction in mortality in the offspring of P2+ pigs, compared to the offspring of mixed-parity sows (see opening article in this Blueprint, page 6).

And some have suggested that vaccinations against mycoplasma and many mass treatments can be eliminated in the P2+ offspring as a result of parity segregation. This allows interventions to be focused on the P1 offspring which represent 20-25% of the total pig flow.

However, there are no peer-reviewed, published data to support these anecdotal field reports. There are several controlled studies currently being conducted to confirm the many field experiences that indicate reduced need for vaccination and disease control measures in P2+ progeny.

Operating Parity Segregation Systems

The goal of a parity segregation system is to separate gilts, through the first farrowing, from P2+ sows. This separation is typically done by housing gilts and P2+ sows on separate sites in order to keep the gilts from transmitting disease to the P2+ sows. There is no agreement on how far the sites need to be separated to achieve the health benefits.

There are also several projects currently investigating whether the benefits of parity segregation can be achieved with the gilts and P2+ sows housed on the same site (similar to an on-site, off-site concept where the separation distance may consist of several hundred yards or more).

With parity segregation, the timing of the movement between farms varies between different systems. In some systems, the P1 sows are moved to the P2+ farms at weaning; others breed the weaned P1 sows at the gilt farm, then move them to the P2+ farm after confirming pregnancy (typically 40 to 60 days of gestation).

The gilt farm is sized to house all of the unmated gilts, breeding and gestating gilts and farrowing for all P1 sows. The total amount of breeding/gestation space required is determined by how long after weaning the P1 sows will be maintained in the gilt farm system.

The following are a few examples of different parity segregation system designs:

  • If the system is expecting an annualized 50% replacement rate, then the gilt farm will require about 25% of the total system capacity, assuming that P1 sows will be moved at weaning.

  • If P1 sows will be held until the middle of their second gestation, then the gilt farm will require between 30% and 35% of the total system capacity. The gilt farm would typically have isolation barns for incoming gilts. Many of the existing systems do not have an isolation barn for the P1 sows moving from the gilt farm to the P2+ farms.

However, in several systems, adding an isolation barn on the P2+ farm has reduced the risk of disease transmission from the gilt farm to the P2+ farm. This approach requires that sows be moved between farms on a periodic basis, instead of weekly, which does not fully utilize gestation space at the gilt farm. The approach does, however, lower the chance that disease would be moved between farms.

Should the gilt farm become infected with a new disease, the backup plan would be to move healthy, unmated gilts from gilt development into the P2+ farm to allow the depopulation or disease elimination from the gilt farm.

Also, the offspring from the gilt and P2+ farms would be moved to separate grow-out sites in separate trailers. These movements create two separate flows for growing pigs.

There have been several systems that have remodeled existing facilities to parity-segregated flows, and in these systems there is one gilt farm and several P2+ farms. The size of farms in these systems has been adapted to meet the existing facilities.

At least one new system has been constructed to allow for additional farrowing capacity at the gilt farm in order to increase lactation length at the gilt farm, relative to the P2+ farms. This accommodation was made to take advantage of the larger response in P1 females to increasing lactation length relative to P2+ females. This design allows for optimization of return on fixed assets across all parities.

One of the challenges with parity segregation is whether the concept is best suited to large systems. To investigate its value in smaller systems, there are several studies either planned or being conducted that are looking at the benefits of separating offspring by dam parity that were farrowed on the same farm.

In addition, there are unanswered questions about the separation necessary for the growing pigs in order to gain the benefits of parity segregation. The goal of these studies is to understand if the growing pig benefits of parity segregation can be achieved without the cost of separating the sow and growing pig facilities. This adaptation of parity segregation would allow all farms, regardless of size, to be able to achieve the benefits of parity segregation.


Parity segregation is a natural evolution of the pig flow strategies that the industry has employed. The placement of gilts on one site and P2+ sows on another location has proven to be a reliable way to increase the stability of performance in sow farms and lower weaned pig cost.

In addition, there appears to be significant improvements in growing pig performance when pigs are separated from the gilt and P2+ sow farms.

In the next year, as more systems adopt parity segregation and research is published, the best methods to implement parity segregation and the potential benefits of this production method will be further elucidated.

Factors Threaten Strong Hog Prices

Surprisingly strong hog prices this spring are tempered by three threats, says Purdue University Extension marketing specialist Chris Hurt.

The first threat is that pork exports won't be able to prop up hog prices after this spring. The second is that old-crop soybeans won't last. And the third is that bad weather will further drive up feed costs.

For the first quarter of 2004, pork production has climbed 2%, yet prices have jumped a remarkable 25%.

“The obvious conclusion is that demand is substantially better this year,” says Hurt. “The most logical explanation would rest with outstanding export shipments as a result of the sharply restricted beef exports due to bovine spongiform encephalopathy (BSE) and reduced broiler exports since February due to bird flu.”

Offsetting demand is a forecast of 20.3 billion lb. of pork for 2004, up 1% over last year's record. Slaughter is projected higher this spring and summer, driven by a 3% larger supply of pigs under 120 lb. on March 1, based on the Agriculture Department's last Hogs and Pigs Report.

Also driving higher slaughter numbers is the escalating influx of Canadian pigs, says Hurt. Through mid-March, about 1.9 million head were imported from Canada, including both pigs and slaughter animals, pushing Canadian imports to nearly 10% of U.S. slaughter.

“There remains some chance that pork supplies will drop modestly late in 2004 and early 2005 as U.S. producers indicate they intend to farrow 1% fewer sows this spring and 2% fewer sows this summer,” he says. “However, if Canadian supplies remain at current levels, these reductions may not show up as reduced pork production.”

Trade uncertainties over BSE and when broiler exports will resume complicate hog price forecasts. At this point, Hurt predicts hog prices will average $41-45/cwt. over the next 12 months.

Corn and soybean meal futures prices suggest cost of production will exceed hog prices by $2/cwt. during this time period.

Lean hog futures prices on March 29 averaged about $46.50 on a cash hog basis for 2004, about $3.50 above live price predictions. Hurt strongly suggests producers investigate forward pricing or selling lean hog futures as pricing options.

Age, Parity Impact Breeding Traits

A major portion of the potential benefit of parity-segregated management of sows is due to enhanced reproductive performance. This article will highlight differences in reproductive physiology and performance between gilts, first-parity (primiparous) sows, and second-parity or greater (multiparous) sows in an attempt to identify areas where parity-specific management might help increase reproductive efficiency.

We will also address other key management issues that may have reproductive implications for parity-segregated systems.

For example, there are periods during the reproductive cycle when it is less risky to move females from the gilt farm to the mature sow farm.

Age vs. Parity

For recordkeeping purposes, sows are categorized based on their parity, which is simply the number of litters they have farrowed. Parity is positively correlated with age, but it is important to recognize the two are not directly linked. Differences in the rate that gilts reach puberty, as well as pregnancy failure in some gilts and sows followed by rebreeding, result in considerable variation in the age of sows within a specific parity category.

Based on sow farm production records, reproductive performance generally increases over the first three to four parities, then begins to decline as sows reach the seventh or eighth parity.

It has often been assumed that this initial boost in performance is related to the maturation of some components of the sows' reproductive system. However, there is little evidence of parity-based differences in female reproductive processes such as estrus, ovulation, fertilization and embryo survival. This may be partially due to the fact that few studies have focused on the underlying causes of this change in reproductive performance.

In addition, experiments rarely separate the effects of age and parity. This makes it impossible to determine if differences observed between parity groups were due to the aging process, repeated reproductive cycles, or some combination of these two factors.

It is possible that physiological differences in the reproductive systems of gilts and primiparous sows could be responsible for their decreased reproductive performance compared to multiparous sows.

However, retrospective comparison of the reproductive performance records of groups of different parity females almost always ignores the fact that these groups are not comprised entirely of the same individuals. It is quite possible that reproductive failure of sub-fertile gilts and first-parity (P1) sows removes them from the breeding pool, and in effect increases reproductive performance of the group in the subsequent parity. This natural culling process may be the primary reason that reproductive performance gradually increases over the first three to four parities.

Wean-to-Estrus Interval

Parity 1 sows, and in some cases second-parity (P2) sows, take longer to return to estrus after weaning than sows of third or greater parity. Primiparous sows often exhibit a 0.5 to 2.0 day longer wean-to-estrus interval than multiparous sows.

The size of this wean-to-estrus interval difference depends on a number of factors. Average daily feed intake during lactation is often 2 to 3 lb. lower in primiparous sows compared to multiparous sows. Primiparous sows also have fewer body reserves to mobilize during lactation than multiparous sows because they are still growing toward their mature size. This increased energy demand for body growth and lactation, combined with decreased feed (energy) intake in primiparous as compared to multiparous sows, may result in a greater negative energy balance.

The resulting catabolic (energy imbalance) state inhibits the secretion of hormones that drive the growth of ovarian follicles and delays the postweaning return to estrus. Suckling of the litter is also a potent inhibitor of hormone secretion and follicle growth, and primiparous sows may be more sensitive to these negative effects than multiparous sows.

Sows that take seven to 10 days to return to estrus after weaning often have decreased farrowing rates and litter sizes compared to sows that return earlier. Primiparous sows are more likely than multiparous sows to exhibit such a late return to estrus. Nutritional programs aimed at development of gilt body reserves, and at maximizing the feed intake of lactating, P1 sows, may help minimize this problem. Parity segregation would definitely make it easier to implement such nutritional programs.

Farrowing Rate

Gilts typically exhibit a 10 to 15% lower farrowing rate than multiparous sows. Primiparous sows also have a 3 to 5% lower farrowing rate than multiparous sows. Farrowing rate remains relatively constant from the second through P5 or more, and then begins to decrease significantly around P7 or P8. The lower farrowing rate of gilts and primiparous sows may be due to the presence of more sub-fertile females in these groups than in higher-parity groups, in which subpar females have already been culled.

However, bred P1 sows that return to estrus and require a repeat breeding do not seem to have a higher rate of recurrence of repeat breeding at the P2 and P3 level than P1 sows that do not require a repeat breeding. Litters that result from a repeat breeding tend to be about 0.5 pigs larger than litters that result from no repeat breeding.

These findings add support to the argument that P1 sows that fail to conceive or remain pregnant should get at least one more chance.

Litter Size

Litter size is generally lowest at P1, increases up to P4 or P5, then tends to level off until it begins to decrease around P7 or P8. A P2 “dip” in litter size has been evident in some sow farms. The body condition of P1 sows at farrowing and their management during lactation likely play major roles in whether litter size dips in P2. Parity segregation would allow the body condition of immature females to be more closely managed.

Estrus and Ovulation Timing

The duration of standing estrus is about five to 10 hours shorter in gilts compared to sows. There is considerable variation among farms and individual females, but duration of estrus typically averages 40 to 45 hours in gilts and 55 to 60 hours in sows.

A sow's duration of estrus and onset of estrus-to-ovulation interval are inversely related to her wean-to-estrus interval. In other words, sows that have short wean-to-estrus intervals (three to five days) tend to have a longer duration of estrus, and a longer onset of estrus-to-ovulation interval than sows that have long wean-to-estrus intervals (six or more days).

Given that primiparous sows tend to have longer wean-to-estrus intervals than multiparous sows, it is to be expected that they would have a shorter duration of estrus and a shorter onset of estrus-to-ovulation interval.

In some cases, this difference in wean-to-estrus interval may be large enough to justify a quicker administration of artificial insemination (AI) services after detection of estrus in primiparous as compared to multiparous sows (Figure 1). Gilts clearly warrant a more rapid administration of AI services after detection of estrus compared to sows due to their shorter duration of estrus.

Parity-segregated farms would have the advantage of being able to customize heat check and AI protocols to better fit the shorter duration of estrus in gilts and primiparous sows, compared to the longer duration of estrus in multiparous sows. Such specialization could improve the reproductive performance of gilts and primiparous sows.

Ovulation and Fertilization Rate

The number of eggs released at ovulation (ovulation rate) increases in gilts with each successive estrous cycle, especially in gilts that reach puberty at a young age. This is one of the reasons for recommending that mating be delayed until the second or third estrous cycle in gilts. Sows do tend to have a greater ovulation rate than gilts, but it is not clear if ovulation rate increases over the first four to five parities as litter size does.

There is some good evidence that age, not parity, is the factor that influences ovulation rate and litter size. Regardless, ovulation rate is so high in the prolific genotypes currently in use that it does not limit litter size.

Once eggs are shed at ovulation, they are viable for only about eight hours. On the other hand, sperm can remain viable in the oviducts for 24 hours. This is the primary reason why gilts and sows need to be inseminated prior to ovulation (Figure 1). When insemination occurs within 24 hours prior to ovulation in sows, the percentage of ovulated eggs fertilized (fertilization rate) tends to be high (85% or greater), regardless of parity.

Gilts, on the other hand, seem to require a narrower insemination-to-ovulation interval than sows to achieve a similarly high fertilization rate. Therefore, while one AI service each day of estrus is usually sufficient for sows, gilts may benefit from two AI services each day they are in estrus. Segregation of gilts and P1 sows would make adoption of such specialized AI protocols more feasible.

Embryo and Fetal Mortality

Given the increase in litter size observed up to P4 or P5, one would expect an increase in prenatal (embryo and fetal) survival to account for this change. However, the percentage of embryo mortality during the first 30 days of gestation, before uterine capacity becomes limiting, and the percentage of fetal mortality after 35 days of gestation, when uterine capacity can become limiting, does not seem to differ significantly between gilts and sows. It is possible that an increase of fetal survival (uterine capacity) is responsible for the increase of litter size up to P4 or P5. At present, studies are lacking that have specifically investigated the effects of parity on embryo or fetal mortality.

For maximum reproductive success, movement of P1 sows from the gilt farm to the mature sow farms should probably not occur within the first 30 days postbreeding. Stress during this period can reduce embryo survival. P1 sows could be moved to the mature sow herd either at weaning or after 30 to 40 days postbreeding.

Nutritional Effects on Reproduction

High levels of prebreeding and postbreeding feed intake can affect ovulation rate and embryo survival, but they seem to have different effects in gilts, primiparous and multiparous sows. High prebreeding feeding levels can increase ovulation rate, but this so-called “flushing” effect has mainly been observed in developing gilts and does not generally improve litter size.

In addition, nutritional regimens that increase ovulation rate may also decrease embryo survival, particularly when a high level of feeding is continued postbreeding. Several studies have demonstrated that a high feeding level during the first 10 to 15 days postbreeding decreases progesterone concentrations, and embryo survival in gilts and primiparous sows, but not in multiparous sows.

In contrast, other studies have failed to find a negative effect of high postbreeding feeding levels on embryo survival in gilts or primiparous sows. While it may be a sort of cheap insurance to restrict feeding of gilts and primiparous sows for 10 to 15 days postbreeding, it has not been clearly established that this is necessary.

Lactation Length

Average lactation length on U.S. sow farms currently stands at about 18 days, with ranges of 14- to 22-day lactation lengths probably common within a group of sows.

Primiparous sows are more susceptible than multiparous sows to the increased wean-to-estrus interval and decreased farrowing rate associated with lactation lengths less than 21 days.

In contrast, P1 and P2 sows were less susceptible to reduced litter size at lactation lengths less than 21 days than were P3 or greater sows (in some studies).

Still, from a sow reproductive performance standpoint, it might be ideal to avoid lactation lengths less than 18 days for the primiparous sows in the gilt sow farm. While segregation from multiparous sows would make this possible, it may not be practical, depending on the flow and requirements of the system.

Table 1. Typical Lactation and Postweaning Reproductive Characteristics of Gilts, Primiparous Sows and Multiparous Sows
Gilts Primiparous Sows Multiparous Sows
Parity 0 1 Ž 2
Farrowing body weight 440 lb. 500 lb.
Farrowing 10th-rib backfat 0.8 in. (21 mm) 0.7 in. (18 mm)
Lactation avg. daily feed intake 9-12 lb. 13-16 lb.
Wean-to-estrus interval 5-6 days 3-4 days
Duration of estrus 40 hours 47 hours 57 hours
Estrus-to-ovulation interval 28 hours 33 hours 40 hours
Ovulation rate (no. of eggs shed) 18-23 20-25 22-27
Fertilization rate 80-85% 85-95% 85-95%
Embryo mortality 30% 30% 30%
Fetal mortality 15% 10% 10%
Farrowing rate 75-80% 80-85% 85-90%
Litter size, total born 10.5-11.5 12.0-13.0
Litter size, born alive 9.5-10.5 11.0-12.0

Seasonal Infertility Problems

A seasonal decrease in sow fertility during the summer and early fall is a common and costly phenomenon in many sow farms. From July to September, sows take longer to return to estrus after weaning, and there is a higher incidence of anestrus than at other times of the year. Sows mated during this period typically exhibit a 10% decrease in farrowing rate and sometimes exhibit a 0.5- to 1.0-pig decrease in litter size compared to sows mated during the spring and winter. Extra gilts are usually mated in an attempt to meet farrowing targets.

There is often an increase in irregular returns to estrus (greater than 24 days postbreeding) in sows mated during the period of seasonal infertility. This seems to be related to the failure of some sows to respond to embryonic signals and complete maternal recognition of pregnancy. The fact that these types of failures result in complete rather than partial embryo mortality may explain why a reduction of farrowing rate is more commonly observed than a reduction of litter size in sows mated during the period of seasonal infertility.

Primiparous sows exhibit a greater increase in wean-to-estrus intervals than multiparous sows during the summer period. However, gilts, primiparous sows, and multiparous sows mated from July to September all exhibit a similar decrease in farrowing rate compared to the other three quarters of the year.

Analysis of some records indicates that P1 and P2 sows are less susceptible to reduced litter size during the summer than third or greater parity sows, though the reason is not known.

Lactation feed intake can be reduced during the summer months, and primiparous sows would be the most adversely affected by such a deficiency. This might explain the greater increase of wean-to-estrus intervals in primiparous sows in summer.

Parity segregation would certainly make special feeding of primiparous sows easier. However, there is no other clear advantage of parity segregation in meeting breeding targets during the period of seasonal infertility based on our limited knowledge of the system flow.


Despite the fact that gilts and primiparous sows have significantly reduced reproductive performance compared to multiparous sows, there is little evidence of any substantial differences in the physiology of the reproductive process between these parity groups (Table 1). This may be due to a lack of experiments designed to specifically examine the effects of age and parity on reproductive processes.

Conversely, the increase in reproductive performance from gilts through the first few parities may be due in part to the removal of subfertile females from the breeding herd and not to some physiological change. Primiparous sows have lower lactation feed intake, longer wean-to-estrus intervals, an increased incidence of anestrus, and decreased farrowing rate and litter size compared to multiparous sows.

Parity 1, and to some extent, P2 sows, are more susceptible to increased wean-to-estrus intervals and decreased farrowing rates than P3 or higher-parity sows after short lactation lengths.

During the period of seasonal infertility, primiparous sows exhibit a greater increase in wean-to-estrus intervals, but a similar decrease in farrowing rate compared to multiparous sows.

High levels of feed intake postbreeding may exert differential effects on embryo survival in gilts and primiparous sows vs. multiparous sows.

Parity-specific AI schedules may be beneficial given the longer wean-to-estrus interval, shorter duration of estrus, and shorter onset of estrus-to-ovulation intervals of primiparous as compared to multiparous sows (Figure 1). Given the shorter duration of estrus in gilts as compared to sows, it is clear that administration of AI services to gilts should not be delayed after the onset of estrus has been detected.

Global Pork Positioning Study

Differentiating U.S. pork from competitors to help global customers make more informed purchasing decisions and to grow U.S. market share are key elements behind the Global Pork Positioning Study.

The U.S. Meat Export Federation (USMEF) and the National Pork Board jointly sponsor the study.

“Identifying the key messages about U.S. pork that resonate with international consumers was the idea behind this study,” says Tom Lipetzky, USMEF vice president, international programs. “It's critical we develop unique positioning and messaging that enable global consumers to quickly identify that U.S. pork is a superior product — great tasting, high quality, nutritious, safe — and a good value.”

Research was conducted in Japan, Mexico and Poland, surveying consumers on what message was most well received in each market.

“The research demonstrates that consumers were strongly influenced by messages that the U.S. pork industry has the most rigorous quality standards in the world, and that our producers use highly nutritious, well-balanced feed to produce a wholesome, tasty product,” he explains. Ads are running in several magazines based on themes developed from these strengths, and consumer feedback should be available in a few months.

Lipetzky notes USMEF is building on traditional strengths while working to create new export opportunities.

Components Of Parity Segregation

The evolution of the swine industry over the past 20 years has been quite phenomenal. Techniques like segregated early weaning (SEW) and three-site production were not in existence at all 20 years ago, yet they are probably the gold standard of pork production today in North America.

In the beginning, the dream of SEW was disease elimination. But in reality this technique is much more of a disease control technique than a disease elimination technique. The improvement in productivity was probably related to the true application of the all-in, all-out (AIAO) principle, and also the specialization of both staff and site.

Parity segregation aims to take those AIAO and specialization principles one step further to enhance the productivity of the overall system.

Defining Parity Segregation

There are basically two components to parity segregation: sow herd and progeny/offspring.

At the sow herd level, parity segregation is the segregation of gilts and first-parity (P1) sows from the older, second-parity and above (P2+) sows. The segregation of P1 sows can be done any time after a sow weans her first litter, and before she farrows her next and becomes a P2 sow.

For the progeny of the sow, the goal is to achieve complete segregation between the offspring of the P1 sows and the offspring of all the other parity sows.

As with SEW and multi-site production systems, many options could exist within this general definition based on production goals, production status and problems to be solved.

In consequence, during the implementation of parity segregation, animals could be moved at different times of their cycle and many different scenarios would exist.

Figure 1 summarizes the five main components of parity segregation. Within those five main production points, other subcomponents could be added based on needs. Keep in mind that there may be advantages from using only a part of the total parity segregation system.

In the first system where we developed parity segregation, the steps outlined below were followed:

  • Early gilt exposure to the pathogens in the production system;

  • Segregation of gilts during the rearing process;

  • Gilt breeding and gestation;

  • Farrowing of P1 sows and rebreeding;

  • Introduction of P1 pregnant sows as replacement animals in the “old sows” breeding herd; and

  • Complete flow segregation of the P1 and P2-plus offspring.

Why Parity Segregation?

The original driving force for the establishment of parity segregation was in response to all of the problems related to gilt development, introduction, gestation and farrowing.

Based on the lessons learned from three-site technology, it was thought that this concept of segregation could be pushed one step further to enhance gilt development.

Advantages and reasons for parity segregation can be divided into three groups:

  1. Focus on gilts — Parity segregation will allow pork producers to raise gilts properly — providing them with the right feeding program, the right building and the right amount of space to grow properly.

    After gilts have been grown out, it's crucial to focus on their final development. Parity segregation will ease the implementation of programs that support proper backfat deposition on gilts and provide adequate boar exposure. These are critical to final reproductive development of gilts.

    Regrouping gilts in one building with dedicated staff will allow for better estrous detection and make specific matings easier.

    When all gilts are farrowed in the same barn, a specific lactation diet can be fed to take into account the normal lower feed intake during the first lactation.

    And, it's a well-known fact that first-parity sows act completely different at weaning than older sows do. Regrouping the P1 sows will make usage of specific programs and mating patterns easier.

  2. Health advantages — Gilts can often be a destabilizing factor when they are introduced into a herd. In a designated gilt grower barn, having animals of the same age with a prolonged acclimatization period greatly helps to reduce the risk of destabilization in mature sow herds when P1 gestating sows are introduced. Gilt introduction normally acts as a destabilizing factor on most farms.

    With parity segregation, herd health is stabilized, even in older sow herds dealing with porcine reproductive and respiratory syndrome (PRRS) virus.

    Health problems related to gilts and their progeny at first farrowing are common. Undoubtedly, gilts and their progeny carry a lower immune status. Therefore, gilts are generally more susceptible to diseases like mastitis-metritis-agalactia (MMA), and their piglets are more prone to scouring.

    Regrouping all gilt farrowings in one location makes the implementation of disease-specific prevention programs much easier.

    However, using parity segregation to control Mycoplasmal pneumonia in progeny from first-parity females has struggled. The problem seems to disappear in progeny from P2 and older sows without the aid of vaccination.

    For example, in one system looking at slaughter check lesions for enzootic pneumonia, a three-fold reduction was seen in the severity of lesions in the progeny of P2 sows vs. P1 sows. In that system, no vaccinations medications were used on the P2 progeny, and both were provided to the P1 progeny.

  3. Management advantages — Another advantage to regrouping all gilts on a given farm allows for the development and use of more specific equipment.

For example, producers could use narrower and shorter gestation crates, as well as narrower farrowing crates. Because we know we will have to deal with prolonged wean-to-first-service intervals in P1 females, more space can be provided in the breeding square, or hormonal therapy may be applied more aggressively.

Weaning weights of gilt progeny are normally lighter than those of older sows. This is probably due to lighter birth weights and to lower feed intake. Lower weights at weaning will usually result in lower weight gains in nurseries and finishers.

Keeping P1 litters together allows producers to design a system that builds in the extra space needed to reach optimum market weights while reducing variation within a barn.

Parity segregation can also help achieve consistent throughput. Designing a production system that allows gilt production to be segregated and maximized provides for a consistent supply of quality gilts into the breeding herd, enabling weekly farrowing targets to be met week after week.

Better Pigs Through Progeny Segregation

Assessing the advantages of the offspring in a parity segregation system is not always easy. We have already mentioned some of the health advantages related to PRRS and mycoplasma control. Table 1 describes the differences in production seen between the P1 offspring and the P2 offspring in a given system over a two-year period. In this case, the advantages of the P2 offspring over their P1 counterparts add up to a $2.50 advantage.

Specifically, offspring segregation has:

  • Allowed us to stabilize PRRS in the progeny. Today most nursery batches from the mature sow herd are negative for PRRS at the end of the nursery phase.

  • Helped us to stabilize PRRS in the mature sow herds we oversee, where there hasn't been a PRRS break in the past three years.

  • Improved control of mycoplasma. Vaccine is no longer used on the progeny of the P2-plus sow herd, while a strong vaccination program is still needed on the P1 progeny. As described earlier, lesions due to enzootic pneumonia have been reduced three-fold for the P2 progeny at slaughter.

Table 1. Production Results for Parity 1 and Parity 2+ Progeny
Item Parity 1 Offspring Parity 2+ Offspring
Nursery mortality (%) 2.96 1.52
Nursery ADG (lb./day) 0.95 1.03
Nursery drug cost (US$) 1.37 0.53
Finisher mortality (%) 3.8 3.25
Finisher ADG (lb./day) 1.75 1.81
Finisher drug cost (US $) 1.07 0.77
ADG = average daily gain

As a caution, the figures for the two progeny groups in Table 1 were obtained from side-by-side comparisons, and do not provide a good basis for results obtained prior to the split of the two groups. However, a retrospective analysis of the records of that enterprise indicates that the results obtained today with P1 offspring are similar to those obtained when the two progeny groups were raised together.

Transportation costs of offspring segregation are not included in the cost structure.

All in all, there still appears to be a real cost of production advantage to using parity segregation on the offspring of P1 and P2-plus sows.

Gilt Acclimatization and Development

One of the main goals of parity segregation is to focus on the gilt. Even with parity segregation, producers must pay close attention to acclimatization and development of gilts. This process has three main components — an exposure phase, a cooling-off phase and a final development phase.

Exposure phase — In the vast majority of the industry today, replacement gilts are healthier than the receiving herd. Therefore, gilts must be exposed to the pathogens of the receiving herd. This exposure needs to be done as early as possible to make sure the potential setback caused by the pathogens will not interfere with sexual development and subsequent reproductive performance of the gilts. With PRRS, for example, we know that the development of immunity might take longer, so the exposure should occur as early as possible.

This exposure can be accomplished by direct animal contact, by exposure to animal tissue or by the injection of infected serum. Usage of commercial vaccination or medication programs could also help in gilt development and immunity.

For direct animal contact, our recommendation is to raise replacement females in a continuous-flow (batch system) nursery. For each nursery pen of 10 to 20 gilts, place one growing pig derived from the progeny of P1 females. Belief is that the P1 progeny carry a more representative sampling of pathogens in the system. The replacement animals should be kept up to 70 days of age in the nursery exposure phase.

Cooling-off phase — After animals have been exposed to a specific pathogen, they could shed that organism for a period of time. To avoid re-infection of the existing herd, it is very important that any replacement gilts introduced to a herd are not shedding.

This makes the cooling phase after exposure very important. Depending on the targeted disease, this cooling-off phase could be up to 120 days.

The cooling-off or quarantine phase provides an opportunity to finish the gilt development process. A proper feeding program should maximize protein deposition up to 135-140 days of age, then maximize backfat deposition.

For this phase, we place gilts in a small, isolated finishing barn from 70 days to 150 days of age, maintaining group integrity and providing 10 sq. ft./gilt of space.

Final development phase — After 150 days of age, the gilt enters the final development phase. Between 150 and 190 days of age, the diet should maximize backfat deposition. During this period, direct boar contact is advised. Animals should be kept isolated during this phase as well. The goal is to breed the gilt at her second detected estrus, when she should weigh 297-308 lb. with a backfat of 16 to 18 mm (.64 to .72 in.) and be 200 days of age or older.


We are still in the infancy of understanding all the pros and cons regarding parity segregation.

However, the results obtained so far make this breeding/reproduction strategy attractive, and we expect to learn much more about its benefits within the next few years.

Risks Related to Parity Segregation

We have mentioned many advantages related to parity segregation, but as with any strategy, there are also risks and pitfalls related to the application.

First, parity segregation reduces the flexibility in a system. After the implementation of parity segregation and the use of P1 females as replacement animals for the older sow herd unit, the system becomes much more of a continuous-flow system and animals need to be moved on a regular basis. This reduces flexibility, mainly in the face of a disease outbreak.

The other danger of parity segregation is related to the biosecurity risk posed by making the use of isolation units at each sow farm much more difficult to implement. However, if off-site gilt acclimatization is done well and the cooling-off phase properly set, this phase could easily become the isolation period for each group of animals.

Parity segregation in a system under expansion is more difficult to apply. When establishing a new herd, due to the fact that replacements will be brought in as P1s, we need to plan replacement matings at the same time that we are doing matings for herd establishment. This will increase the number of gilts needed and the space needed for the production of those animals.

Exposure to pathogens is also critical. Our goal is to expose animals to herd pathogens early to enhance herd health stabilization. If for some reason proper pathogen exposure does not occur, there is the possibility of introducing naive animals and placing the receiving herd at risk of infection.

Parity segregation increases the number of movements for animals, adding to transportation costs and increasing the risk of contamination.

Location also needs to be taken into consideration. The scientific community does not agree on proper separation distances between gilts, P1s and their offspring and the rest of the system. We recommend a minimum separation of two miles. Each pyramid should also have a dedicated transportation fleet.

With replacements being produced in a common location, a disease break at the site could potentially transfer problems to every production location.

Tracking Maternal Line Differences

Improving sow herd production levels is one of the most challenging aspects of pork production. Herd production levels depend on many related, interdependent factors that can frustrate even the best managers. Taken together, these factors often have a multiplier effect on total output. Small improvements in several measures can mean large economic returns.

Better Reproductive Selection

Selection for reproductive traits, such as prolificacy and fertility, is almost entirely in the genetic supplier's control. Commercial pork producers are not prepared to deal with the extra expenses incurred when intense selection for lowly heritable reproductive traits is practiced.

The genetic supplier's role will increase as genetic markers become more important in selection programs. The most important genetic decision for the commercial pork producer targeting improved reproduction is which maternal sow line to use. It is the genetic difference between sow lines that is important.

The genetic component of reproductive efficiency is only 10-20% of the variation within a genetic line. However, commercial producers can control some environmental factors, such as nutrition, herd health and housing, which account for 80-90% of the reproductive variation.

Most commercial producers require replacement females to meet some minimum individual standards for herd entry, whether they are purchased or produced internally. Since replacement gilts and gilt acclimation programs are expensive, only leg soundness and fertility standards are generally used.

Environmental Interactions

A source of producer frustration can be a genetic lines' sensitivity to environmental interactions. These may become more important when the within-line genetic component is small. This sensitivity can affect how a genetic line performs for different producers.

An extreme example would be ranking wild pigs vs. the improved maternal lines in commercial production. In the wild, it is best to have a few large pigs per litter rather than a large litter of smaller pigs. And, it is best to conceive only when the litter would be born in good weather. In the wild, these females are likely to raise more live offspring per year than their commercial counterparts. However, in a commercial setting, the improved maternal lines would surely outperform sows acclimated to the wild.

Genetic suppliers constantly face the challenge of determining the type of environment in which to raise and select their foundation lines. Their current practice is to provide a very high health, intensively managed production environment for foundation line animals.

Commercial producers may have difficulty achieving these same high herd health and management levels. Producers may also be tempted to decrease feed costs by using lower nutrient levels than recommended by their genetic suppliers.

Table 1. Gilt Loss During Growing/Development Period
Outcomes of gilts not taken to sow units at 165 days of age
Reason No. of gilts Percentage of gilts entered to wean-to-finish
Death 163 4.6
Umbilical hernia 49 1.4
Injury 19 0.5
Unthrifty 36 1.0
Other 9 0.025
276 7.75%

Table 2. Summary of Gilts Not Meeting Breeding Criteria
No. of gilts Percentage of gilts taken to sow units
Abnormal tracts 21 0.6
Quit cycling 52 1.6
Not cycling 242 7.3
Normal cycling 108 3.3
Pregnant 4 0.1
Unknown 6 0.1
Total gilts slaughtered, head 433 13.1

Table 3. Genetic Line Differences of Age at First Estrus and First Farrowing (Parity 1)
Gilt age at first estrus and first farrowing
Line No. of gilts % showing estrus Age at first estrus (days) % of gilts farrowing Age at farrowing (days)
American Diamond Swine Genetics 562 91 225 77 371
Danbred USA 541 87 222 77 366
Monsanto DK44 550 87 222 75 367
Monsanto GPK347 547 97 209 92 354
National Swine Registry 515 90 222 77 367
Newsham Genetics 568 88 223 78 368

Modern commercial maternal lines may have specific environmental sensitivities such as disease resistance, nutritional requirements and seasonal breeding cycles. These sensitivities are affected by the foundation genetics used to develop maternal lines and the type of internal selection program followed. All genetic lines trace back to a few superior animals. The unique differences between the foundation animals become properties of the resulting genetic line.

Therefore, successful sow management requires knowledge of how a specific sow genetic line interacts with the environment and procedures they will face in the commercial operation.

Gilt development programs, breeding herd efficiency and sow lactation management are all factors of herd production that can be adjusted to improve output of a specific genetic sow line.

Maternal Sow Line Program

The National Pork Producers Council conducted the National Genetic Evaluation Maternal Line Program (MLP) from 1997 through 2000, which provides examples of some interactions as well as parity effects that result from between-line genetic differences.

The goal of the checkoff-funded MLP was to evaluate six genetic sow lines for reproduction, growth, carcass and meat quality traits through four parities. Gilt grower/development records and breeding performance records were collected through six parities.

Genetic lines studied were American Diamond Swine Genetics, Danbred USA, Monsanto Choice Genetics (two lines: DK 44 and GPK 347), National Swine Registry Yorkshire x Landrace F1 crossbreds and Newsham Genetics. Each line was represented by about 600 females.

The 3,600 gilts were delivered at 10-20 days of age and grown in wean-to-finish barns before being placed in two new, 1,600-sow, breeding-farrowing-lactation facilities at about 165 days of age (150 days in wean-to-finish).

The attending veterinarian, wean-to-finish unit manager and NPPC program manager jointly evaluated gilts for health and abnormalities at approximately 165 days of age. Culling of gilts prior to delivery to the breeding site was limited to the following criteria:

  • Chronic illness or injury as determined by the attending veterinarian.

  • Extreme light body weight for age that indicated a chronic problem (three standard deviations from genetic line mean).

About 3% of the gilts were culled for umbilical hernias, chronic illness and severe injuries. Gilts were not culled for growth or backfat thickness. The number and percentage of gilts culled for various reasons are shown in Table 1.

To enter the test, gilts had to conceive on their second or later observed estrus, after they were 205 days old and before 300 days of age. The 3,283 gilts entering the two sow facilities were exposed to vasectomized boars daily from 165 to 300 days of age. All matings were done by artificial insemination (AI) using fresh semen from one unrelated sire line. Gilts not meeting the breeding standard were slaughtered.

Reproductive physiology specialist Don Levis of the Ohio State University evaluated the reproductive tracts of culled gilts. Most of the gilts were not having estrous cycles at slaughter age, which was at least 330 days (Table 2).

Table 3 shows the genetic line differences in age at first estrus and age at first farrowing. The GPK 347 line was youngest at both first observed estrus and first farrowing. Likewise, in addition, a higher proportion of GPK 347 gilts were mated and conceived. The combination of these fertility traits reduced open days in the sow herd.

An important design requirement of the MLP was that no gilt or sow could be culled for poor reproductive performance (small litters, poor milking, etc). The only way that a female could leave the program was death, injury or failure to conceive within 50 days of weaning. Fertility problems were the most important cause of involuntary culling.

The amount of daily gestation feed given each sow was determined by her postweaning weight and desired weight gain before next farrowing. Litters were crossfostered within 48 hours of birth, standardizing the number of pigs nursed at about 10.

All sows were fed three times daily during lactation in an effort to maximize feed intake. Daily lactation feed disappearance for each sow was recorded. Average weaning age was 15.4 days.

Results of the MLP show that the Monsanto GPK 347 females ate less feed in lactation and lost more weight and backfat thickness during lactation. General observation would suggest this line would perform at a lower reproductive level. However, as the results in Tables 4 and 7 show, the reverse was true. The GPK 347 females actually produced more pigs born per litter and per sow lifetime. In the confinement environment of the MLP, the GPK 347 had very few fertility problems at Parity 1 and 2 (P1 and P2). That single factor gave the line a tremendous advantage in longevity. Differences between other sow lines were not as large.

Parity Management

The MLP results in Table 5 show the challenges and opportunities for managing genetic lines and parities differently.

Parity 1 females had as many pigs born as Parity 3 (P3) and Parity 4 (P4) sows, were smaller at farrowing, lost more weight and backfat during their first lactation and ate less feed.

However, not all genetic lines had a significant drop in P2 performance. A few lines had differences between Parities 3 and 4, American Diamond increasing and Danbred decreasing in number of pigs born per litter.

Extending gilt development programs through mating for P2 litters may offer significant benefits. Clearly, if young females are to grow and reproduce successfully, they must meet certain nutritional and health goals. Even though the MLP females had increased gestation feed allotted for growth, these sows did not return to the same body composition at P2. The sows were larger but had less backfat depth. There may be an advantage to feeding a P1 gestation diet to bred gilts that increases longevity.

Table 4. Total Number of Pigs Born per Litter, Genetic Line by Parity Interaction Means
Genetic Line Pigs born Parity 1 Pigs born Parity 2 Pigs born Parity 3 Pigs born Parity 4
American Diamond Swine Genetics 10.09 9.90 10.16 10.72*
Danbred USA 11.10 10.74 11.52* 10.77*
Monsanto DK44 11.59 11.44 11.56 11.66
Monsanto GPK347 12.19 11.86 12.03 11.82
National Swine Registry 11.08* 10.23* 10.79* 10.37
Newsham Genetics 10.61 10.37 10.50 10.61
*Indicates statistical difference (P<.05) between parities for total pigs born.

Table 5. Differences in Performance Between Parities
Parity Total pigs born Sow weight at farrowing, lb. Sow lactation weight loss, lb. Sow backfat at farrowing, in. Sow lactation backfat loss, in. Litter birth weight, lb. Litter wean weight, lb.
1 11.08 453 53.2 0.82 0.07 34.9 100.8
2 10.79 493 47.0 0.77 0.05 37.8 112.3
3 11.14 516 45.8 0.74 0.04 37.8 111.1
4 11.08 533 46.1 0.71 0.01 37.3 107.2
Means with a common superscript are not different (P<.05).

Table 6. Parity-to-Parity Loss of Females by Line
Genetic Line Parity 1 %* Parity 2 % Parity 3 % Parity 4 % Parity 5 % Parity 6 %
American Diamond Swine Genetics 23 13 7 7 10 10
Danbred USA 23 14 7 8 9 13
Monsanto DK44 25 10 8 7 11 7
Monsanto GPK347 8 9 6 7 7 12
National Swine Registry 24 13 6 5 9 11
Newsham Genetics 22 13 6 7 9 13
*Percentage of entered gilts that never farrowed a litter

Management skill is a key factor in recognizing and maintaining gilt fertility. Some managers are better at recognizing gilts in heat. Having these managers work only with gilts may greatly increase the farrowing rate of gilt matings.

Litter birth weights and weaning weights were smaller for P1 females. Pigs weaned from P1 litters are smaller and may have less maternal immunity to disease.

Another management opportunity may be to segregate P1 pigs through nursery and finishing periods. Extending gilt development programs to P1 weaning or P2 mating makes P1 pig segregation easier.

Sow Longevity Barriers

Results of Table 6 show that the greatest barriers to sow longevity are gilt and post-first-parity sow losses due to infertility. The major component of sow loss prior to 450 days of age is reproductive failure.

Gilts that are never serviced or fail to conceive reinforce the difference between the GPK347 line and others prior to 300 days of age.

Many producers fail to account for the cost of days on feed and facility space occupied by these gilts that do not have breeding records. The National Pork Board's Production and Financial Standards require entering all gilts into the sow herd when they are delivered or selected. Litters and/or pigs per sow year ratios will be lower due to increased open gilt development days when these standards are implemented. A parity-segregated management system will include all gilt development days in its reports.

Table 7. Production of 130 Cohorts Through Six Parities
Genetic line Total sow days Avg. sow life, days Total pigs born Total pigs born live Live pigs/sow day Total litters born
American Diamond Swine Genetics 14,138 566 835 758 .054 79.7
Danbred USA 13,632 545 860 767 .056 76.9
Monsanto DK44 14,009 560 944 843 .060 80.5
Monsanto DK347 17,197 688 1,312 1,172 .068 109.0
National Swine Registry 14,033 561 871 790 .056 80.6
Newsham Genetics 14,230 569 870 790 .055 81.4

Table 8. Six-Parity Output Among the 130 Maternal Line Program Cohorts
Trait Best cohort Worst cohort Goal
Total litters born 127 40 150
Live pigs born 1,347 397 1,575a
Avg. sow life, day 781 358 900b
Total sow days 19,542 8,957 22,500c
a10.5 live pigs born per litter
bSow life days start when gilt is entered to gilt developer, 170 days of age.
c900-day life times 25 sows

Keeping management records of groups of females (cohorts) entering the sow herd on the same dates will account for all bred and open sow days used. A cohort is “a group of animals that share a common event within a defined period of time.”

Cohort management allows animals to be grouped several ways. The MLP gilts were randomly assigned to 25 gilt cohorts by genetic line-sow unit-age group when delivered to sow units. The MLP cooperator herds allowed NPPC to follow the sows through P5 and P6 reproduction measures. All days in sow units are included, from gilt entry at 165 days of age, until weaning of P6 litters.

Table 7 shows the large differences in herd output for the GPK 347 line, which was superior in age to first farrowing, proportion of gilts conceiving, proportion of P1 females conceiving and number of pigs born per litter. Together these traits give a great advantage in total pigs born and sow life.

Sow Herd Potential

There is tremendous biological potential for increased sow herd output. This may not be good news for hog market prices, but pork producers have no choice but to continue improvements to remain competitive.

Table 8 shows the large range in cohort production in a carefully recorded, side-by-side comparison of genetic lines. Improvements of 20-30% more pigs from a sow herd are suggested by these data. Individual producer management and cost structures are needed to find the most profitable herd production level.

Choice of a maternal sow line is the major genetic decision for commercial producers. The next decision is how to maximize that sow line's potential in the production environment at all sow ages.

Extension of gilt development through first parity may give “multiplier” benefits to the mature sow herd if gilt fertility and sow longevity are improved.

Segregation of P1 litter pigs in nursery and finishing may also increase net returns.

Rodney Goodwin was director of the Maternal Line Program for the National Pork Producers Council.

Pork Quality Revisions

The certification period for the Pork Quality Assurance (PQA) program has been extended from two to three years.

Currently, nearly 79,000 U.S. pork producers are certified in PQA Level III. All of those over age 18 will be granted an additional year to their current certification.

The PQA program was launched in 1989 to ensure a safe, wholesome food supply.