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Articles from 2004 In October

Detailing Depop-Repop Cleanup Strategies

Depopulation and repopulation (depop-repop) have long been recognized as a successful and reliable means to eradicate disease. The cost of downtime in depop/repop, however, has been a limitation to its use in disease eradication programs.

Making the decision to depopulate and repopulate a herd is a difficult one that must be well thought out to understand both the cost and potential benefits.

It may be a relatively quick decision, such as if a new disease breaks in the herd — porcine reproductive and respiratory syndrome (PRRS), pseudorabies (PRV), Actinobacillus pleuropneumonia (APP), swine dysentery — or after long-term frustration with chronic diseases.

Reasons to Depopulate

Disease eradication is the primary reason for herd depopulation. Besides eradication, depopulation is expected to decrease mortality and medication costs and improve average daily gain and feed efficiency.

Depopulation has been successful for many different diseases, and can be used to rid an operation of multiple diseases simultaneously.

Depopulation and repopulation are the fastest, most reliable ways to return the herd to high-health status. This can be particularly vital in multiplication herds or any farm that needs to quickly reestablish its health status.

Herd location is a key factor in the decision, because it will determine the odds of the project being a long-term financial success. If the herd is in a good, fairly isolated location, the decision to depopulate is easier vs. a farm located in a very pig-dense area, which is likely to become reinfected with the disease.

Swine Vet Center staff has developed state maps from aerial photos identifying all the local hog farms to help evaluate area risk, identify where to do off-site breeding projects and for routing pigs (Figure 1).

Parity distribution of the herd can be another reason to consider depopulation. There can be a number of reasons for parity distribution becoming heavily weighted with older-parity females. If the goal is to eradicate a disease from the herd, and if herd parity distribution is older, then the decision to depopulate makes more sense.

Genetics is another argument for depopulation. This is a good opportunity for rapid genetic improvement, and can help offset some cost of upgrading herd health with better performance in the offspring.

The U.S. swine industry has changed to predominantly Isowean production units, easing the process of depopulation. Downtime is dramatically reduced because pig age variation is less on sites.

As D.L. (Hank) Harris, DVM, described in the first Blueprint article (Multi-Site Systems Broaden Protection, p. 6), the purpose of Isowean production was to eliminate the need for herd depopulations. But it has actually made depopulation easier and less expensive due to the separation of production sites.

For a depop-repop to be successful, gilts of the proper health status and in adequate numbers must be on hand. Health status and genetic quality must match up well enough for production and in products sold at market.

Whether to depopulate in a high or low market is a long-standing debate. If cull sow price is high, more of the cost of replacement gilts can be offset, even though the cost of replacement gilts will likely go up as well. The timing and effect of downtime must also be considered in relationship to the market price.

There is always risk in depopulation, so financial impact must be considered. Each producer must evaluate the financial impact if the depopulation fails and the herd rebreaks during the depopulation or soon after. This can be a financially devastating blow.

Planning is Critical

Once the decision is made to depopulate a herd, the hard work of developing a good plan begins. Adequate time devoted to the planning phase can really help to ensure success. It's best to plan a year ahead, but 4-6 months is the minimum to make sure everything is organized.

Evaluate the overall production flow and assess project breakdown into manageable parts. This is easier to do in multiple-site systems and minimizes downtime.

For multiple sow farms, decide if all farms will be depopulated at once or if they should be done in phases.

If done in phases, the best place to start is at the multiplication level, so that internal replacements can be made as soon as possible.

If the system has multiple farrowing sites, and the project will be done in phases, use existing inventory in farms that have yet to be depopulated. This reduces the cost of gilts on farms yet to be sold off. This also allows the system to make better use of the younger parity animals in the herd to be depopulated, rather than just sending them to slaughter. Mixing these herds is always a risk, but generally, if gilt introduction stops, the herds stabilize and herd health may even improve before depopulation.

Breeding of the new herd can be done on-site or off-site. On-site projects require more downtime (20 weeks average). Off-site projects will allow minimal downtime for production (30 days for the sow farm).

Off-Site Breeding Project

There are several factors to consider when developing an off-site breeding project.

Isowean farms are not a big concern since they don't impact the downstream sites at the same time.

Nursery and grow-finish run all-in, all-out by site, and are relatively easy once you get past the sow farm site.

To be able to accomplish this minimal downtime goal, there will have to be an off-site gilt-breeding project. This requires a site that can hold the sow herd inventory. Using 15 sq. ft. stocking density, this will generally require two times the normal finishing capacity. For example, a 2,400-sow farm will need 5,000 head of finishing capacity.

Site location for biosecurity must be as good as the sow farm to reduce project risk during this phase. The mapping software (Figure 1) can help identify sites at risk. Be sure to:

  • Provide people access to the site.

  • Ensure there are shower-in, shower-out facilities.

  • Allow space to breed animals in the barns.

  • Provide some temporary housing for boars, and put some crates in a pen to house boars separately. The best success has been to heat-check and group gilts that are in heat into a pen. Breed gilts 21-42 days after they have been regrouped. This has resulted in the best conception rates for breeding and gestating in pens.

Financial Impact of Depop-Repop

Using a partial budget is a good way to evaluate the impact of a depopulation-repopulation program.

It's important to make sure that as many costs as possible are accounted for, because many unforeseen costs can creep into the system.

Building a spreadsheet model is a very good way to run different scenarios throughout the model. Running an optimistic and pessimistic model will satisfy everyone on the production team as well as the lender. Important items in the partial budget include:

  • Cost of replacement stock (including freight, royalties and all other charges).

  • Cost of the off-site breeding project.

  • Finishing space costs. Include cost of space, cost of lost opportunity of finishers sold, cost of additional space if rented, and cost of deciding if finishers will be marketed at a lighter weight because of space limitations.

  • Unit staffing. Are there employees available to work on the project, or will there need to be more training of new employees?

  • Important biosecurity measures. Be sure to consider downtime of employees between sites, separate transport and clean and/or dirty stock.

  • Cost of repairs and maintenance of facilities while empty.


There are many benefits to the depop/repop cleanup process. It can benefit sow herd performance, but has a negative effect on production during the startup phase, including gilt performance and the effect of using off-site facilities.

Long-term production benefits include increased pigs produced and better herd efficiency.

Grow-finish performance is improved by lower mortality, improved average daily gain, feed conversion and space requirements.

Once the model is developed, it can be refined to meet the unique features of the project to more accurately predict the outcome from depopulation-repopulation.

Remember it is just a model, and is designed to give an overview of the project. Don't spend too much time modeling the project; spend more time planning.

Observations of Herd Depopulations

The most common observation after depop-repop is: “I didn't remember raising pigs could be this easy and fun again.” Improvements can be expected throughout production, from farrowing through finishing. The magnitude of the change depends on the herd's status before the depopulation.

One disappointing point has been in herds depopulated for PRRS. A number of them have broken back with the disease over time. From sequencing information, it's clear that none of the herds have broken back with the original herd strain. The survival time chart (Figure 2) shows the rate of breakback in herds.


Making the decision to depopulate and repopulate is never easy. Once the decision is made, planning the depopulation/repopulation becomes a very important task. If things are done well, the odds of the project being successful are high. This takes time and organization as well as good communication with all members of the production team.

It requires everyone thinking of as many details as possible, taking the time to come up with the best solutions to problems.

Keep the project document as a living document. Updating it as the process goes along is essential to the success of the program.

Maintaining good communication with all team members, and keeping them informed and updated regularly, will help make sure that small details are not missed or forgotten.

If planning and execution of the plan are done properly, the project will be successful and the goals achieved.

Developing Plans for Cleanup, Restocking

Outlined below are steps for cleanup, developing a written plan, identifying replacements and restocking the farm.

The site will need to be cleaned, disinfected and fumigated just like the main herd, but before the project begins.

The site will also need downtime before population, but that will depend on the history of the site.

Pest Control

Set up the pest control program for the farm so numbers can be reduced as much as possible at depopulation. Use professional exterminators for the best results.

Written Plan

  • Develop a detailed, written plan.

  • Outline every project that needs to be done in both the new and old herds.

  • Note dates that projects must be done.

  • Color-code or use a marking system to clarify which system has responsibility.

  • Build the schedule around the delivery date to keep the rest of the project dates in line.

  • Provide time in the schedule to evaluate and repair all equipment, and order all parts and materials ahead of time to prevent delays.

  • Keep the project as a living document that is updated as changes occur.

  • Develop a detailed plan for the depop-repop (Table 1).

Source for Replacements

Identifying a source for replacements should be one of the first steps in the planning process, since this may determine the timetable of the depopulation.

Make sure there are plenty of gilts available (equal to 20 weeks' worth of inventory). Have at least 5-6 weeks worth of the breeding target so there is enough inventory of the proper age to cycle, and meet breeding targets without having to dip into younger gilts, which will decrease herd performance.

Make arrangements to take all the various ages of gilts in staged population so that the entire population is in place when the project begins, to avoid any changes in the health status of the source farm during the project.

Once you've found a source of suitable replacements that meet genetic and inventory needs:

  • Do a vet-to-vet communication (your herd veterinarian contacting the source herd's veterinarian).

  • Conduct serologic monitoring to make sure there are no subclinical diseases in the herd. Monitor both finishing herds and sow herds for differences between the populations. Testing a statistical sample of both (usually 30 sows and 30 finishers) will give a good picture of the farm. A standard set of diseases to monitor would include PRRS, Mycoplasmal pneumonia, swine influenza virus, TGE/PRCV and APP.

  • If possible, arrange a visit to the source farm.

  • Audit the biosecurity practices at the source farm. Explain the project to the source farm staff so they can understand what you are trying to accomplish and can help the farm meet its goals.

  • Meet with staff in charge of transportation so they understand the importance of the project and their role in its success.

  • Audit transport procedures and truck washing to make sure they are not putting the project at risk.

  • Plan a route to ship pigs that minimizes the risk of contact with gilts being transported to the off-site breeding farm. The mapping program can be useful here.

  • Design the delivery schedule to get the herd in place as soon as possible so the isolation period can begin.

Old Herd Cleanup Plan

Work ahead, because old herd cleanup is a bigger job than anyone realizes. As soon as areas are empty, clean them up. Other steps include:

  • Understand that one cleaning won't be good enough.

  • Remove all organic matter.

  • Inspect washing after the barn is dry.

  • Have someone else inspect the area each person has cleaned.

  • Use a flashlight to check quality of cleanup after it has dried.

  • Use sidewalk chalk to mark problem areas; it marks well but washes off easily.

  • Carry a screwdriver and putty knife to check the hard-to-get-at areas, and make sure they are clean.

Problem areas include beams that slats sit on, joints in between the slats, tops of feed lines, and electrical conduit and plumbing lines.

The most important thing is to plan enough time for everything to get dried out completely.

Site Repairs

Depopulation is an excellent time to do site repairs. Plan this activity well in advance of the actual depopulation so work can be scheduled and repairs ordered to avoid delays once the site is emptied. Larger projects may start before depopulation. Advantages to repairs during depop are that workmen don't have to work around the pigs, and biosecurity is easier before the cleanup is complete.


Disinfection of the site is a crucial job prior to herd repopulation.

Downtime is one of the best things we can do, plus having everything clean and dry. Summer months prove best due to less cost to dry things out, and less heating cost while leaving the facilities sitting empty.

The most common downtime is four weeks, but some projects have been done in as little as one week. This is a herd-by-herd decision based on pathogens to clean up and the level of risk the producer is willing to accept.

The site should be disinfected once it is washed and has passed inspection.

Getting everything dry is probably the best disinfectant.

Remove any standing water left after washing (i.e. water troughs, etc.). A leaf blower can be helpful for this job.

Most projects have been double-disinfected followed by fumigation.

Make sure disinfectants used are different classes of compounds so the widest range of coverage can be achieved (i.e. disinfect with Tektrol and Synergize, then fumigate with formaldehyde.).

The site should completely dry between applications of disinfectants.

Fumigation should be scheduled just prior to the animals returning to the site, leaving just enough time for the facility to air out thoroughly and be rinsed down before refilling.

Fumigation will also help to kill any other pests (rodents, insects, etc.).

Restocking Plan for the Farm

Transportation is important to make sure the project isn't put at risk.

If using farm trucks, be sure vehicles are cleaned using the same guidelines as the farm. Trucks must be separated into new herd and old herd to avoid cross-contamination; use separate truck washes.

Map out the route to deliver the new inventory to the farm from the off-site breeding project. Check the route for farms to decide if changes need to be made.

Review farm biosecurity protocol and make the necessary upgrades to keep the disease eradicated.

Table 1. Detailed Plan for Depopulation-Repopulation

Red denotes activities with the herd and site being depopulated. Black denotes activities with the new herd.
Date Week Month Activity
2/8/2002 6 2 Breed last group to farrow at home farm (2/11/2002).
2/15/2002 7 2 Clean and disinfect off-site project. Fumigate the off-site project (2/25/02).
3/1/2002 9 3 Populate off-site project with new gilts.
3/8/2002 10 3 Begin vaccination of select weight gilts.
Empty out isolation (3/11/02), clean up as soon as possible and double-disinfect.
3/15/2002 11 3 Begin breeding the new gilts (3/19/2002).
3/22/2002 12 3 Begin booster vaccination of select weight gilts.
3/29/2002 13 3 Heat check the first new herd heat checks, and then continue the heat checking on a weekly basis. Give booster vaccines to gilts that have been vaccinated. Receive the last shipment of gilts from Canada (3/27/02).
4/19/2002 16 4 Breed last group in the old herd (4/20/02). Fumigate at the Isowean barn (4/18/02). Conduct first preg-check of new herd breeding, then check the following week.
4/26/2002 17 4 Cull sows that are bred and will not farrow before the depopulation date (sows bred after 2/11/2002). Then cull the wean sows after they have had a chance to dry up. Take new gilts to the isolation barn (550 head) (4/22/02).
5/3/2002 18 5 Consolidate sows to the breeding barn. Begin cleaning the gestation barn.
5/17/2002 20 5 Get gestation barn ready for disinfection. Test isolation barn and take necessary gilts to the breeding site.
5/24/2002 21 5 Reload isolation to hold 550 head.
5/31/2002 22 5 Breeding barn cleaned and ready for disinfection. Farrow the last sows in the old herd (5/29/02).
6/7/2002 23 6 Depopulated all animals, and clean and disinfect the last two farrowing rooms. Wean the last pigs from the site (6/6/02). Totally depopulate the site by 6/7/02. Prefarrow vaccination for new herd, then continue on a weekly basis.
6/21/2002 25 6 Give second prefarrow vaccinations for the new herd, then continue on a weekly basis.
6/28/2002 26 6 Fumigate home farm (7/1/02).
7/5/2002 27 7 Repopulate home farm (7/5/02). Close up females and gilts from isolation barn loaded first.
7/12/2002 28 7 Begin farrowing new gilts (7/11/2002). Reload the isolation barn (550 head).
7/26/2002 30 7 Wean the first group to the nursery or wean-to-finish barn.

Fifteen Herd Health Lessons

You enter your production facilities and immediately sense that something is not right with the herd. It's quieter than normal; few animals stand. Over 10% of the animals aren't eating, even though there's ample water.

Walking the barn, you note a few abortions, a slight cough. Your veterinarian inspects the animals, collects blood and tissue samples for laboratory submission, and recommends waiting for the diagnosis before taking any action. He offers words of encouragement, yet you still feel a sense of desperation.

Frustration mounts with more abortions, more coughing, too many sows dying and unthrifty pigs. This scenario becomes the norm as the disease becomes endemic within the herd. Vaccine and medication costs mount.

Unfortunately, this is a frequent scenario that begs the question: “What is the best system for health maintenance for your farm or system?”

This article examines health management systems and explores disease dynamics, including predisposing conditions using a series called “lessons learned.”

Lesson #1

Health cannot be protected by one approach because one program does not fit all. Health is a complex equation that becomes even more complex when factoring in disease dynamics within populations, variations in management, individual animals and environmental effects. In basic terms, epidemiologists describe these interactions as the disease triad: host, environment and pathogen.

Described mathematically, disease in the animal is inversely proportional to animal resistance, and directly proportional to pathogen load (challenge dose) and pathogen virulence.

Likewise, health is the inverse of this equation and is easily understood at the individual animal level. But, at the herd level, disease becomes much more complex. Epidemiologists use equations to quantify how different risk factors contribute to the likelihood of disease occurrence. Contributing to disease are the animal number, infectious agent, pathogen virulence, organic matter and auxiliary host. Contributing to health are downtime, drying, temperature, pressure, light, vaccines, chemical inactivation and antimicrobials.

For example, some pathogens are very contagious (possess the capability to spread) and others are not; some are highly infectious (possess the capability to cause infection) and others are not.

Porcine reproductive and respiratory syndrome (PRRS) is not a highly contagious organism, yet it is highly infectious (a small amount of the virus can establish infection in an animal).

Because PRRS is not highly contagious, it is easy to understand why naïve animals can be present in herds, particularly large herds with high replacement rates. Because it is highly infectious, it is easy to understand why small amounts of the virus, such as those found in contaminated trucks or needles, can cause infection.

It also helps us understand why crossfostering piglets between litters enhances PRRS spread within farms, and why mixing infected and non-infected pigs at weaning has devastating consequences.

In contrast, salmonella are very contagious, yet not highly infectious. Thus, salmonella are easily spread and present on many if not most farms. Yet they infrequently cause disease because very large numbers are required for infection.

This lesson teaches that while designing a system to control one disease may be easy, designing one to address multiple agents is challenging because pathogens are not created equal. Comprehensive disease control programs must feature control measures for all pathogens and management and environmental factors.

Lesson #2

Comprehensive biosecurity systems are by nature complex, difficult to design and very hard to administer — and they are critical. One mistake on a single day by a single person can bring disaster, which is why many biosecurity systems fail. They lack focus, appear difficult and typically are not adequately explained, and therefore are not fully implemented.

To simplify matters, control measures should be segregated into those that are best controlled at the system level and those that are best controlled at the farm or local level. Both are of equal significance, yet it is important that only the daily critical elements remain at the local level. This approach removes many concerns typically controlled at the farm level.

Figure 1 is a fishbone diagram illustrating this point. Health is dependent on components that should be assigned to system level control (the top branch) and those that should be assigned to local control (the lower branch).

Systematic measures are those that should be designed and managed by someone who is not typically present on the farm every day, yet has the time and expertise to accomplish key biosecurity elements. This person focuses on the design of the health program and then monitors replacement and semen sourcing protocols, isolation and acclimation and vaccination and medication.

In contrast, local control addresses issues such as traffic control, transport sanitation, vector control and dead animal disposal. This division makes biosecurity programs less cumbersome and allows for accountability.

Lesson #3

Limit breeding stock sources. Closing herds to new animal infusions has great potential to limit disease risk. However, when impractical, limit sources to as few as possible. As the number of replacement and semen sources increases linearly, disease risks increase exponentially.

Lesson #4

Isolation and acclimation of incoming breeding stock are essential. It is common knowledge that isolation for incoming breeding stock is needed for observation and testing. Veterinarians now recognize that acclimation is also crucial to reduce the pathogen load circulating within the breeding herd. Through vaccination or exposure to pathogens, incoming replacements will hopefully become immune or minimal shedders before entering the herd. The proper time interval and best way to stimulate immunity are farm- and pathogen-dependent.

Lesson #5

Most pig diseases come from other pigs, so the first step is to limit exposure to other pigs (see Lesson #3).

Second, limit exposure to “pig elements” which can be found on the bottom of worker boots and on clothing, hands or hair. At a minimum, staff and visitors should only wear farm-provided boots and garments and wash their hands before entry. Just washing hands between rooms can impact transmission of disease within farms.

Taking this concept further, work by Sandy Amass, DVM, Purdue University, suggests that shower-in, shower-out is needed to fully prevent farm-to-farm transmission of diseases such as E. coli associated with neonatal diarrhea.

The direction of people traffic is also important. Figure 2 depicts a health pyramid. Ideally, there should be no traffic between the pyramid elements. But if necessary, flow should only be from the point of greatest potential harm to the point of least potential harm (boar stud toward finishing) and not in reverse.

The amount of downtime between units is a hotly debated subject among veterinarians. While everyone agrees that it has benefit and the interval is farm- and system-dependent, it is the interval length that is argued.

For example, 48 hours of downtime may be required to visit elements at the top of the pyramid, while little or no downtime may be required for finishing units. Obviously, variation in health status is the key determinant for site visits. No one should go from sick herds to healthy herds.

Lesson #6

Distance is often the best means of keeping disease out. One of the great failings of current production systems in the U.S. is the location of sow units close to nursery-finishing facilities. Aerosol, insect and vermin have been linked to numerous outbreaks of disease between closely located units.

For example, epidemiology models in Europe and the U.S. suggest that pseudorabies (PRV) and foot-and-mouth disease can be spread farm-to-farm by aerosol, with wind and humidity playing significant roles. It is likely that other diseases are spread by aerosol, too.

Insects can play a key role in farm-to-farm transmission of disease. This has been reinforced recently in work by Scott Dee, DVM, University of Minnesota. Insects play a role in mechanically transmitting PRRS between farms. In Dee's study, PRRS-carrying flies were found over two miles from the farm where they came in contact with infected animals. Flies can also harbor Transmissible gastroenteritis (TGE), PRV, hog cholera virus and Streptococcus suis.

Mosquitoes are also a real concern, though they harbor PRRS for less than six hours.

Lesson #7

Because disease can be easily transmitted between farms, siting becomes a vital biosecurity concern. During the 1970s and later, many production systems built facilities, including sow units, near packers without regard for disease spread.

Figure 3 depicts how the U.S. system is currently configured with sow, nursery and finisher units clustered around a packer. Many now recognize this mistake. Sow units have been repeatedly infected, even after depopulation/ repopulation, parity segregation or closed herd technologies have been applied.

The low cost of hauling young pigs to finishers in the Corn Belt from sow units on the grain belt fringe can easily offset the recurring cost of disease within sow herds.

For this reason, we propose that a more reasonable system segregates units by type of production (Figure 4).

Lesson #8

Sanitizing facilities is more dependent on cleaning, drying and downtime than is disinfection in managing total pathogen load. Although disinfecting is the most-discussed aspect of sanitation, Table 1 demonstrates that proper cleaning, drying and downtime are much more important.

This is not to diminish the importance of disinfecting, but to emphasize that front-end preparation is vital for it to be effective.

One of the most overlooked aspects of room and truck preparation is drying. The poultry industry has emphasized this point for years. Recent work by Montserrat Torremorell, DVM, of PIC suggests its importance to the swine industry. Placing sows in farrowing rooms still wet from cleaning, and loading trucks that are not dry, negates much of the work effort.

Lesson #9

Selecting the appropriate class of disinfectant is very important. This is actually an old lesson, recently reinforced.

In the past, the focus was on rotating disinfectants to keep them effective. We now know it's more important to select disinfectants based on the infectious agent to be controlled.

For instance, if PRRS is a concern, then gluteraldehyde or quaternary ammonia compounds are indicated; however, if E. coli is the target, choose a phenolic compound.

Lesson #10

Trucks are a risk factor for transmitting disease agents between farms. Truck-sanitizing protocols should be in place and executed to detail. Again, Dee has demonstrated that pathogens such as PRRS and Streptococcus suis can persist on truck tires between farms.

Table 1. Effect of Various Washing Steps
State of house Viable bacteria/sq. cm
Immediately after pig removal 50,000,000
After plain washing 20,000,000
Hot water wash + detergent 100,000
Target before disinfection 1,000

Dee and Amass have also shown that while disinfection of truck tires is beneficial, this step alone only helps reduce tire contamination. Further, it is not a substitute for cleaning the entire vehicle, because it is not uncommon for the interior truck floor to be contaminated, as well as the wheel housing.

If a tire sanitizer is used, its efficacy is highly dependent on environmental conditions.

For example, under warm, dry conditions, tire sanitizers may not be needed because simply driving the vehicle on the road may sufficiently reduce bacterial contamination.

However, in moist and cool conditions, sanitizers help reduce contamination. Again, the selection of the appropriate disinfectant is important (see Lesson #9).

Lesson #11

Animal carcasses for incineration, composting material or the dead pig pile are often visited by buzzards, rats, possums, raccoons and other scavenging wildlife. For this reason, mortality disposal should be considered one of the greatest risks to herd health, and disposal units should be operated to discourage vermin visits.

Lesson #12

Footbaths filled with disinfectants are a poor substitute for a brush and water hose if sanitation is truly the goal. With good intentions, many farms place footbaths filled with disinfectant at the entrance to buildings in hopes of preventing the spread of infectious agents between groups.

However, too often this effort fails to achieve the desired result. As Table 1 demonstrates, there is no substitute for removing organic matter to reduce contamination. Once a manure-laden boot enters the footbath, its beneficial contribution is negated.

Most of this article has focused on disease prevention. But it's also crucial to address the other part of the health equation, disease resistance.

Lesson #13

Vaccines are an adjunct to disease control, but to be effective, proper timing and administration are required. Too often, vaccination protocols are built around worker schedules rather than what is appropriate for optimization of pig immunity.

As a case in point, in most situations vaccination of pigs for erysipelas should occur between 8 and 10 weeks of age to avoid maternal immunity interference. However, many nursery operators will begin administration much earlier to spread out the workload. The result may be partial immunity, at best.

Vaccination timing is no longer a cookbook item. It requires full knowledge of disease and immune dynamics within the target population. This requires mapping of disease for serologic conversion and disease occurrence. Using this information, swine veterinary consultants can strategically overlay their understanding of passive immunity duration, risk of disease occurrence, and duration of vaccine protection to optimize vaccine efficacy. Again, this is herd- or system-dependent and cannot be generalized across farms.

Lesson #14

Medication should never be thought of as a substitute for good biosecurity. The pork industry is being closely scrutinized because it is a major user of antimicrobials. Consequently, the Food and Drug Administration has recently changed its regulations governing the animal drug approval process (Guidance Document 152). This new process suggests there will be greater restriction on antimicrobial use by producers and veterinarians.

To protect the pork industry's access to antimicrobials for the prevention, control and treatment of disease, it is imperative that the industry decrease its reliance on drugs and focus more on prevention through good management and disease exclusion. Producers and veterinarians need to justify every antimicrobial use on farms.

Lesson #15

Good husbandry covers a lot of biosecurity errors, but not all. Even the best producers with the best facilities cannot overcome the devastation that disease can cause.

Going forward, the swine industry needs to reexamine the role of health for its effect on the well-being of animals as well as health's contribution to the bottom line.

While animal activists are currently focusing on facility design as the major factor driving animal welfare, producers and veterinarians know that daily care and disease have a much greater impact. Not only does disease affect animal well-being, it can also be the difference between economic survival and demise.

Quality production, cheap feed and market access are still the kingpins driving profitability; however, disease remains a key determinant of farm survival, particularly in this new era of tight profit margins.

Lastly, train new employees to ensure that they understand the whys and wherefores of biosecurity programs so they can be properly carried out. Compliance is crucial.

Multi-Site Systems Broaden Protection

Pig production systems have changed dramatically and new diseases have emerged since the first implementation of isolated weaning (Isowean) and multi-site production in the 1980s.

The introduction of these production technologies brought rapid acceptance and application throughout the world.

However, not surprisingly, implementation was often done incorrectly as concepts and procedures were misunderstood.

This overview will review the scientific bases for multi-site production (Figures 1a-c), maximizing disease control and comparing multi-site production to one- and two-site production (Figures 2a-b) for disease elimination.

Concepts, Procedures

In multi-site systems (three-site; multiple-site; isolated, wean-to-finish;), the breeding, gestation and farrowing (B, G, F) stages of production are isolated from the other stages of production (Figures 1a-c).

It was anticipated this concept of production would cause reduced herd immunity. And, in fact, disease agents such as Haemophilus parasuis, which caused few problems in one-site herds, reemerged as a significant pathogen in multi-site systems.

The recent development of parity segregation compensates for this lack of herd immunity, improving productivity in multi-site systems (See April 15, 2004 Blueprint on Parity-Based Management).

In the late '80s, the major disease threat in the U.S. was pseudorabies (PRV). Three-site production proved to be a valuable tool in eradicating the virus from herds without depopulation.

Based on these early studies, it was believed that Isowean pigs from multiple sources could be mixed. However, multi-site systems that mixed weaned pigs infected with porcine reproductive and respiratory syndrome (PRRS) virus from more than one site (B, G, F stages) experienced a profound drop in productivity.

Unfortunately, it took a few years to learn how to produce negative PRRS pigs by Isowean.

Origin of Microbes in Newborns

Usually, piglets are sterile or microbe-free in the uterus of the dam. Some infectious agents such as PRRS and hog cholera viruses may infect piglets in the uterus.

Normally, the piglet's first exposure to microbes occurs as it passes through the cervix into the vagina of its mother. As pigs pass through the vagina, they become infected with microbes. At birth, more microbial exposure occurs by contact with feces, skin of the dam and facilities.

Some microbes grow on the skin, and others are swallowed by the piglet and begin to establish themselves in the mouth, stomach and intestines.

Infection depends on the health and immune status of the sow, overall sanitation of the farrowing facility, colostrum and milk intake, and comfort level of the pig-rearing environment (stress, temperature and dampness).

Medicated early weaning (MEW) and Isowean are two methods to alter the establishment of the microbial flora in the newborn piglet and decrease disease in multi-site rearing systems (Figures 3a-b).

How MEW Prevents Disease

MEW was developed as an alternative to surgical derivation and has the distinct advantage of avoiding surgery on the donor sow.

In MEW, small groups of pregnant sows (near term) from one or more farms are placed in strict isolation and farrowed (Figure 3a). Ideally, each isolated group of sows is induced to farrow within 2-4 days of one another. The sows are heavily medicated both prior to and during their stay in the farrowing unit.

To ensure elimination of some infectious microbes, and achieve higher levels of colostral and milk immunity, the sows may only be from second or higher parities. Vaccines may be administered to the sows 4-6 weeks prior to farrowing to further increase the levels of colostral and milk immunity.

Soon after birth, the piglets are administered heavy doses of antimicrobials to lessen the chance of sow-to-piglet transfer of microbes. The piglets are weaned at 5 days of age or less into isolated nurseries. Often, piglets continue to be medicated for several weeks after weaning.

For best results, each weaning group should have only a 1-2-day age difference when placed into an all-in, all-out (AIAO) nursery.

The move to grow-finish should be well isolated from farrowing and nurseries.

MEW is far more costly than Isowean, which is far more practical and can be readily applied to any production system. However, for elimination of pathogens like Streptococcus suis type 2, MEW is the method of choice.

How Isowean Prevents Disease

Isowean has many synonyms: modified-medicated early weaning (MMEW), segregated early weaning (SEW), age-segregated weaning and segregated disease control (SDC). I prefer Isowean because it is derived from the phrase isolated weaning, which more clearly describes the technique and differentiates it from MEW.

Early weaning is not a feature of Isowean in that pigs are weaned at an older age away and in strict isolation from the other age groups in a multi-site rearing system.

Isowean is different from MEW because in Isowean, the sows are not removed from the farm and placed in isolation to farrow (Figure 3b). The weaning age of an Isowean pig depends on the pathogens for elimination and varies from 8 days to 4 weeks (Table 1).

However, age variation of farrowing groups should be very narrow, as in MEW. Weaning age should only vary 2-5 days.

In Isowean, sows are usually vaccinated in late gestation, as in MEW, but often are not medicated. Sows should be placed in an AIAO farrowing room and all sows should farrow within a 4-7-day period.

If bacterial or respiratory pathogens are to be eliminated, the piglets should be medicated in nursing and postweaning periods. At weaning, the piglets are moved to an isolated nursery (and subsequently to an isolated finisher) or AIAO wean-to-finish building.

Creating a Disease-Free Isowean Pig

There are many factors involved in successfully creating an Isowean pig free of infectious disease agents present in the dam or the environment. The factors include:

  • Level of immunity in the dam to the infectious agent(s);

  • Level of immunity passively acquired by the piglet from colostrum or milk;

  • Age of piglet at time of infection;

  • Medications given to the dam and/or the piglet; and

  • Overall throughput, sanitation and biosecurity practices on the farm.

The age of the piglet at weaning (and lactation length) may be critical to successful elimination of some infectious agents (Table 1). In general, the younger the weaning age, the more likely the piglet will be weaned disease-free. If a very high level of immunity can be created and maintained in the sows, then this may increase the weaning age required to eliminate a pathogen.

Multi-Site Production Approaches

Multi-site rearing systems rely on Isowean for the production of disease-free weaned pigs residing in the adult population in the breeding, gestation and farrowing site(s). One-site and traditional two-site farms can utilize Isowean by incorporating an isolated nursery and finisher unit for all or part of weaned pig production.

In fact, prior to construction of the first three-site system in 1988, all Isowean experimental trials involving elimination of PRV, toxigenic Pasteurella multocida and Mycoplasmal pneumonia were conducted by removing a portion of the weaned pigs from one site and traditional two-site farms infected with those agents.

Successfully using Isowean to exclude pathogens depends upon many factors. Most importantly, weaning and finishing facilities must not be operated on a continuous-flow basis, since not every weaning group can be expected to be healthy. AIAO nurseries and finishers also have distinct advantages over systems that are AIAO by room or pen within a barn.

There are eight steps to eliminate infectious agents by multi-site systems:

  1. Establish procedures for isolation and acclimation of incoming replacement breeding stock. If the infectious agent has been recently introduced into the breeding herd, it may be necessary to wait until a level of immunity has been achieved in the adults. Furthermore, it may be important to add replacement stock (negative to the infectious agent in question) to the herd immediately following a disease outbreak so that the replacements also become immune to the agent. The length of acclimation is determined by the infectious agent to be eliminated. For the control of PRRS virus, it is imperative that PRRS-negative replacements be utilized.

  2. Vaccinate sows prefarrowing to prevent diseases caused by infectious agents in Isowean pigs. Vaccines are available for microbes such as toxigenic Pasteurella multocida, Mycoplasmal pneumonia, Haemophilus parasuis, Streptococcus suis, Actinobacillus pleuropneumonia, Actinobacillus suis, swine influenza virus and PRV. The use of live-virus vaccines for Transmissible gastroenteritis (TGE) and PRRS virus are not recommended for elimination of these agents by Isowean.

  3. Administer medications to sows prior to farrowing based on the infectious agents to be eliminated.

  4. Establish management steps for AIAO flow for each farrowing room.

  5. Set the weaning age based on the infectious agents to be eliminated (Table 1).

  6. Administer medications to piglets prior to and after weaning based on the infectious agents to be eliminated, using a consulting veterinarian for advice and prescriptions, as required.

  7. Establish management procedures for AIAO throughput for each weaning group in the nursery and finisher.

  8. Maintain strict biosecurity protocols.

Multi-Site's Role in Disease Emergence

The development of multi-site systems may be contributing to the emergence and reemergence of pathogens. Depending upon the infectious agent to be eliminated, the weaning age for Isowean pigs may vary considerably, but is nearly always less than 21 days of age.

The evolution toward multi-site systems has further supported the concept of AIAO production. Weaning at less than 21 days, AIAO throughput and improved hygiene certainly reduce microbial exposure of the piglet prior to weaning in the presence of maternal antibodies.

The result is a requirement in multi-site Isowean systems for high standards of biosecurity to minimize the introduction of infectious agents into grow-finish facilities.

Carlos Pijoan, DVM, and his colleagues at the University of Minnesota have extensively studied the respiratory tract colonization patterns of the bacterial flora of the pig. They list five risk factors for the development of disease due to Streptococcus suis type 2 and Haemophilus parasuis:

  1. Early weaning;

  2. Isowean;

  3. Degree of virulence of the infectious agents in the pig population;

  4. Proportion of sows of lower parity (high numbers of gilt introductions); and

  5. Immunosuppressive infectious agents present in the population (such as PRRS).

Thus, there appears to be an emergence of some infectious agents in multi-site systems, which have not been significant problems in one-site or traditional, two-site farms. Emerging pathogens include Actinobacillus suis, Haemophilus parasuis, circovirus and Strep suis type 2.

Haemophilus parasuis, for instance, was not a significant pathogen in one-site and traditional two-site herds, except when first introduced into a herd. After the initial outbreak of Haemophilus parasuis or Glasser's Disease, adequate herd immunity would develop in most herds and the piglets would be exposed prior to weaning.

Alternately, it has been suggested by Iowa State University researchers Pat Halbur, DVM, and Eileen Thacker, DVM, that herds infected with either PRRS virus, mycoplasma or both may be immunologically suppressed and thus more susceptible to these emerging pathogens.

Due to a lack of epidemiologic knowledge regarding PRRS, the initial introduction of the virus around 1990 into multi-site systems was devastating, and similar (if not worse) than the occurrence of the virus in single-site farms. Subsequently, it was shown that PRRS virus could be eliminated by Isowean in most batches of pigs at a similar rate as via surgical derivation.

In general, PRRS continues to be a serious threat to hog operations. But multi-site farms appear to be able to either eliminate or control the agent better than large, one-site farms.

It is interesting to note that small, traditional, one-site farms appear to eliminate the PRRS virus when effective acclimation of replacement gilts and biosecurity are implemented.

Porcine circovirus type 2 (PCV 2) can be eliminated from pigs by Isowean (Table 1). However, it is unknown if Postweaning Multisystemic Wasting Syndrome (PMWS) can be eliminated or controlled effectively in multi-site systems of production.

Eradication of Infectious Agents

Modern-day multi-site production systems apply Isowean to exclude or minimize infectious agents at weaning to decrease their effect on the performance of the growing pig. The adult population in one-site systems may or may not remain infected with the pathogen(s) eliminated using Isowean.

Prior to the development of Isowean-rearing techniques in the late '80s, eradication methods focused on elimination of pathogens from the entire herd. These methods will be addressed in the following articles in this Blueprint Series. They include: depopulation, cleaning, disinfecting of facilities and repopulation with high-health status pigs, testing and removal of infected animals, and increasing herd immunity or medication.

Although the original intent of multi-site production was to eliminate infectious agents by isolated weaning, leaving Site 1 infected, there have been approaches to also remove pathogens from the entire system. Around 1998, Jorgan Plomgaard, a veterinary practitioner in Denmark, developed a method for eradicating certain pathogens from entire three-site herds. The so-called Plomgaard Method is based on the work of Von E. Zimmermann in Switzerland regarding eradication of mycoplasma from small, traditional herds without total-herd depopulation.

The Plomgaard Method

This technique has been used to eradicate PRRS virus, mycoplasma and Actinobacillus pleuropneumonia (APP) from an entire three-site farm by these four steps:

  1. No replacement of breeding stock for a period of three months;

  2. Whole-herd medication directed against mycoplasma and APP;

  3. Removal of all breeding animals less than 10 months of age and those with no serologic titers to PRRS virus and APP; and

  4. 4.New replacement stock free of PRRS virus, mycoplasma and APP.

These steps resulted in the elimination of the above three swine disease agents from Site 1 of a three-site system. The nursery and finisher buildings at Sites 2 and 3 were depopulated prior to receiving Isowean pigs free of the three agents.

It is likely that PRV and TGE viruses could be eradicated by this method, but it has not been reported as yet.

The efficacy for eradication of specific infectious agents from entire herds is presented in Figure 4.

Depop/ repop is the surest way to eradicate infectious agents, assuming a supply of negative animals is available and the location of the herd is such that reintroduction is unlikely.

However, as compared to the other methods, depop/repop is far more expensive due to the interruption in income when no pigs are being produced or sold. Test and removal, increased herd immunity, whole-herd medication and the Plomgaard Method are only applicable to specific infectious agents, but are not as costly as depop/repop.

As illustrated in Figure 4, many infectious agents cannot be eliminated from the entire herd except by depop/repop. Thus, the clear, main advantage of multi-site production is the capability to eliminate all the infectious agents (listed in Table 1 and Figure 4) by Isowean without the need to depopulate site one (B, G, F stages).

It is up to the producer to design the correct system to take advantage of the power of Isowean to achieve this and thus maximize productivity.

Table 1. Weaning Age Required to Eliminate Infectious Agents by Isowean
Infectious agent Age of Weaning (days)
Actinobacillus pleuropneumoniae 21-28
Bordetella bronchiseptica 10
Brachyspira hyodysenteriae 21
Haemophilus parasuis 10
Lawsonia intracellularis 10
Leptospira spp. 14-16
Mycoplasmal pneumonia 17-21
Pasteurella multocida (toxigenic) 8-10
Porcine circovirus - Type 2 21
PRRS virus 14-16
Pseudorabies 21
Salmonella 14-16
Streptococcus suis type 2* 5
Swine influenza virus 21
Transmissible gastroenteritis virus (TGE) 21
*Medicated early weaning may be required.

Sow and Piglet Immunity

If the dam has been previously infected with a microbial pathogen, it is likely that antibodies will be present in her colostrum and milk, which could aid in protecting the suckling piglet against infection.

However, if the dam has never been infected, and the microbial pathogen is present in the pig-rearing environment, piglets nursing non-immune sows will become infected.

The degree of sow immunity depends on parity, type of rearing system, presence or absence of the infectious agent in the various stages of production, and the type of pathogen.

In general, first-parity sows, and sometimes late-parity sows, may have low or no immunity to a pathogen. One-site and traditional, two-site farms tend to have higher levels of sow immunity because the housing of various age groups of swine in the same air space or in close proximity results in greater transmission and infectious rates of pathogens.

The level of sow immunity can be enhanced by intentional exposure to infectious agents during acclimation of replacement gilts, prior to breeding all sows, and 3-4 weeks prior to farrowing. Some, but not all, vaccines will also enhance sow immunity and aid in the protection of piglets against infection during nursing.

Piglets must receive colostrum within 36 hours of birth in order to absorb protective antibodies. After 36 hours, the piglet's gut closes and these colostral antibodies are no longer absorbed into the blood. The presence of antibodies in the blood is important for protection against certain types of infectious agents like Streptococcus suis, Haemophilus parasuis and erysipelas.

Both colostrum and milk contain antibodies that also help protect the piglet against some enteric infections by coating the mouth, tonsils, stomach and small and large intestine.

Inducing the pig to produce its own antibodies through vaccination or intentional exposure to an infectious agent may enhance piglet immunity.

Ideally, each pig in a farrowing room should be of identical age. In practice, this is difficult to achieve. But in the original medicated early weaning (MEW) experiments, sows were farrowed in isolated farrowing rooms within a 24-hour period.

A variation in the age of piglets in the farrowing room could result in a wide variation in the age at weaning, thus increasing the possibility of lower immunity levels and increasing chance of infection in the oldest weaned pigs.

Management Practices

Administering Medications

Administering medications to both sows and piglets may aid in the prevention of colonization of piglets by most bacterial agents (not viruses).

Sow medications may be given via feed, water or by injection. Piglets must receive medications by oral dosing or injection.

Oral dosing may require 2-3 administrations every 24-hour period. Injectable antibiotics may need to be given every 12 hours or as infrequently as every 3-6 days, depending on antibiotics used and pathogens involved.

Administering medications, particularly to piglets, may increase the weaning age required to eliminate a pathogen.


Overall sanitation of the farrowing room environment will determine the level of infectious agent exposure to the young piglet.

If there is a very high level of pathogens present on floor surfaces, feeding area and in the air, then the piglet may become infected more readily and at a younger age.

All-in, all-out throughput combined with proper cleaning and disinfecting is essential for minimizing the level of infectious agents in the overall pig-rearing environment.


All farms must strive for a biosecure system to lower the introduction of new infectious agents onto the farm or production site. If a new infectious agent affects either farrowing or late-gestating sows, the odds are high that both medicated early weaning and Isowean piglets will be infected with the agent at weaning, primarily due to low or no sow immunity.

Pros and Cons Of Closed Herds Concepts

Closed herd strategies have received renewed attention as producers focus on disease, seen as the largest constraint to profitability, and as technologies to conserve and improve genetics mature.

In essence, the closed herd concept attempts to augment stringent biosecurity by eliminating live animal inputs as opportunities for disease entry into the herd.

Closed herd systems are also perceived to improve gilt acclimation and stabilize herd immunity. This holds true for many typical swine diseases.

The widespread distribution of porcine reproductive and respiratory syndrome (PRRS) virus, due to animal movements, has led producers to consider closed herd systems for risk management and health improvement.

Poor application of closed herd strategies, however, can lead to a loss of genetic basis and destabilization of health. This is especially true in farms endemically infected with PRRS.

Closed herd systems also present challenges in pig flow and require additional management intensity for success. Figure 1 shows typical pig flow for various production schemes using gilt replacements. In Figure 2, pig flow is diagrammed for a closed herd system with internal gilt multiplication.

For their part, external gilt replacement schemes also carry inherent health risks. Persistent or “carrier” disease status confounds diagnostic testing or results in cost-prohibitive testing regimes to ensure gilt health. Gilt introduction without proper herd acclimation can create endemic disease conditions on farms.

Perceptions aside, closed herd systems don't ensure gilt acclimation to sow farm organisms. In fact, poor gilt acclimation schemes are not improved by herd closure alone.

Closed herds do eliminate communication failures between buyers and suppliers about health status of replacement gilts.

Closed herds also remove the risk of disease breaks from newly purchased gilts created by the lag time of diagnostic tests between disease exposure and test results.

Few epidemiological studies have evaluated the difference in disease risk between closed and open herds. Of note, closed herd status was linked to a statistically significant lowered risk for F18 E. coli in a study of Belgium herds.

Short- and Long-Term Closure Strategies

Historically, closed herd strategies have been applied as temporary interventions to control a particular health problem. Closing the herd for a limited time to allow PRRS immunity to stabilize after a break has effectively shortened the duration of disease in farrow-to-wean farms, for example.

These short-term approaches range in complexity, but they do not provide for maintenance of breeding herd inventory and genetic improvement. The duration of these temporary herd closures is limited by the need to replace involuntary culls and sow mortalities, and by the eventual need to return gilt inventory to normal levels. This influx of gilts increases risk of new disease introduction.

Long-term, sustainable herd closure is more complex. It requires a portion of productive females in the breeding herd be replaced with maternal grandparent sows. These sows are mated to maternal line boars (via semen) to produce replacement gilts. These gilts are then reared on site and mated to terminal sires to produce market animals.

Sustaining genetic input is typically accomplished via semen from monitored boar studs supplying artificial insemination (AI) services. Other methods for genetic input that don't require use of live animals, such as embryo transfer, are being developed. However, these new technologies are not widely used because of cost and low efficiencies.

Frozen boar semen may dramatically increase the biosecurity of semen inputs. Frozen semen would allow continued monitoring of the stud while sufficient time passes to ensure that a boar was clear of disease or infection during the collection period.

Pros and Cons

The primary advantages of closed herd systems are tighter control of gilt supply and potential reduction in the risk of disease introduction.

Depending on the structure and pig flow of the system, additional advantages in gilt acclimation can be gained.

But advantages of closed systems carry a cost. Specifically, increased management intensity is required, and group weight and growth rate variation may increase due to management of multiple genetic lines together in nurseries and finishers. Gaps in biosecurity at other phases of production may jeopardize the sow farm when gilts return.

The economic determination of whether to close a herd and internalize multiplication must include these less obvious factors:

  • Reduction in growth rates and marketability of maternal line barrows;

  • Any reduction in market throughput due to devoting space to maternal lines; and

  • Added labor and training costs of handling multiple genetic lines on the sow farm.


Biosecurity is a key prerequisite to starting a closed herd system. The system inherently limits the opportunity for introduction of new genetic material in return for a greater level of protection from new disease introductions.

However, if current biosecurity practices are subpar, the main advantage of the closed herd will be lost. Infections of closed herds (not due to semen) have been reported for PRRS, porcine respiratory coronavirus and swine influenza virus (SIV). Prior to implementing a closed herd, thoroughly review these biosecurity risks:

  • Transportation — Clean and disinfect all transports off site; segregate marketing transports from internal pig movements; eliminate visitor vehicles.

  • Pig flow — All-in, all-out (AIAO) flow maximizes health benefits; segregate/eliminate light pigs that remain on site post-marketing; eliminate rendering visits to sites.

  • People movements — Control order of site visits/work flow; ban visitors; change boots and coveralls, and wash hands between different age/ phase/ health status groups.

  • Equipment use and cleaning — Segregate equipment to barns/rooms and wash and disinfect between groups.

  • Regional risks — Decide if local pig density has contributed to past disease breaks such as SIV and decide if it remains a threat.

While this list is not intended to be all-inclusive, it must be extended to all sites/barns that house gilts returning to the sow farm. Continuous-flow phases tend to serve as reservoirs of disease that impact growth performance, negating the gain afforded by closing the system to outside threats.

Consideration should also be given to the system's disease history. High-health farms using excellent biosecurity and appropriate acclimation on externally supplied gilts are sustainable, given correct relationships and conditions. These production systems may not gain added revenue from converting to an internal gilt multiplication system.

Pig Flow Considerations

Assuming a 50% annual replacement rate, about 3.5% of production will be devoted to producing replacement gilts in closed herd systems.

Another 3.5% of production will be composed of barrows from maternal line litters. Given that they are maternal vs. terminal line progeny, these barrows will increase size variation in growing groups. A plan to manage these barrows is a necessary part of the closed herd system. This can be especially troublesome in the early stages of conversion to a closed herd, when health benefits have not yet offset this growth variation.

In farms under 400 sows, it becomes difficult to introduce similar-aged gilts on a weekly basis, given that gilt demand per week is less than one litter. Batching the maternal litters is an option, but it also introduces variation in gilt age at breeding if a batch of replacement gilts is bred into several different farrowing groups. This requires attention to gilt size and feeding to avoid creating a reproductive problem.

Acclimation is Still Important

In closed systems, acclimation and vaccination of gilts produced internally is as critical, as it is for externally supplied replacements. Ensuring gilt exposure and immunity to sow herd pressures are still necessary.

The immunity desired of a dam is more a reflection of the health challenges for her pregnancy and litter. Vaccination or boostering for reproductive diseases such as porcine parvovirus is frequently still necessary despite previous gilt exposure.

In internal multiplication, gilts shouldn't be expected to provide better lactogenic immunity to preweaned pigs than outside replacements, unless vaccination and exposure are provided during acclimation.

Often overlooked, it is critical that producers understand that a system that poorly acclimates externally supplied gilts will be equally poor in a closed system. Introduction of gilts directly from a continuous-flow finisher barn will make stabilization for PRRS virus elusive.

In PRRS endemic herds, a “cool-down period” is required prior to gilt introductions to the sow herd. This is usually accomplished with a dedicated AIAO gilt acclimation barn.

Experiences with closed systems and recent research would suggest that a closed system where gilts are raised in continuous-flow facilities, then diverted to the sow farm at marketing without an acceptable cool-down period, may actually worsen the clinical PRRS picture on farms.

Though research literature doesn't pinpoint an ideal cool-down period, data on persistently infected pigs suggests that longer is better, assuming this can be accomplished without exposing gilts to other lateral infections.

Moving gilts off the sow farm to three-site or two-site production systems may actually increase risk to the farm when these flows are in pig-dense areas. In these situations, it may be necessary to build facilities to raise gilts on the sow farm site.

Typically, off-site grow-out facilities have lower biosecurity standards, especially if managed AIAO, because of the mistaken belief that any disease will be shipped out with the pigs and not maintained on the site. Incorporating replacement gilts in this flow dramatically changes this perspective, and creates a biosecurity standard for the site equivalent to the sow farm.

And as animals are moved to grow-out facilities off site, transportation biosecurity becomes more important.

PRRS-Endemic Systems

Recently published research suggests the virus can exist in pigs as a “quasi-species” with different genetic strains present simultaneously.

Also, continuous passage of the virus, as occurs in continuous-flow nurseries, leads to genetic variation in the virus. Putting gilts through a continuous-flow, PRRS-infected nursery should not be considered safe.

Managing gilts in smaller, AIAO groups with controlled exposure of the entire group at a single time is preferred. This exposure would be followed by a period of isolation from potential exposure, without new animal introductions, so that immunity of the group is uniform when they enter the sow farm.

Management Considerations

Maternal lines must be identified and managed as a subpopulation in the sow herd. Likewise, the offspring of these maternal females must be permanently identified to distinguish them from market animals. Generally, reproductive performance of maternal sow lines differ from the sow lines used for commercial production.

If the management strategy is to rely on production records to identify changes and challenges to production, maternal performance should be tracked separately from commercial sow performance. Otherwise, this performance variation between the lines can conceal problems. This is especially true in systems using Six-Sigma or statistical process control (SPC) run charts to monitor performance. The increased variation in sow performance can make the methods less sensitive to change.

Closed systems are generally dependent on boar semen to maintain an acceptable rate of genetic improvement. However, in doing so, this foregoes improvement that could be obtained by critical selection of females.

A selection or indexing strategy for maternal line gilts is necessary to ensure improvement. These strategies, however, imply that an excess of maternal gilts will be available for evaluation. The residual (non-selected) gilts are then marketed as commercial animals. As with maternal barrows, these may add variation to growth rate and performance in grow-out phases and/or weight variation at marketing.

In marketing situations that involve a narrow target weight or percent lean, increased variation in finisher pigs is usually dealt with by marketing over an extended period of time. Depending on flow pressures, this can create a continuous-flow scenario on the finisher site, and it might expose maternal gilts, destined for the sow farm, to disease from market trucks and biosecurity lapses.

In this context, growth variation in closed systems can be self-perpetuating if it leads to disease introduction affecting growth.

Endemic Disease in Closed Herds

Herd closure strategies help maintain and improve herd health by eliminating live animal introductions.

Health improvement stems from the ability of herd closure to stabilize immunity and eliminate active diseases. This process is based on the belief that exclusion of naïve animals will eventually result in the whole population having sufficient immunity to prevent disease.

The perception that simply closing a herd will allow immunity to stabilize and eliminate most diseases may be too optimistic. Research shows that Actinobaccillus pleuropneumonia, rotavirus, Streptococcus suis, salmonella and ileitis can persist in closed herds that are actively farrowing.

There are some big assumptions, outlined below, that must be understood to improve understanding and success:

Assumption #1: “No new naïve inputs are added to the population.” The immune status of an animal is not a static state and, in fact, almost always changes over time. An example that is important to closed systems is the piglet with declining maternal antibodies. Eventually, these piglets become naïve animals in the population. Strategies to manage these pigs before they become a risk include segregated early weaning and other early wean strategies that move them off site before they are susceptible to infection.

Another important example is compromised adult animals. A sow with previous exposure and well-developed immunity may not be able to protect herself from infection if she is immunocompromised.

Factors compromising immunity include poor nutritional status, negative energy balance, and other immunocompromising diseases and environmental stressors such as extreme temperatures.

Assumption #2: “Animals develop sufficient immunity to disease to prevent survival and replication of the disease-causing organism.” Disease organisms differ in the degree of response they illicit from the immune system.

Field studies and controlled research have shown that some organisms can persist in the animal in a carrier state. These organisms, such as salmonella and PRRS virus, survive in the animal despite the immune response mounted.

In contrast, “sterilizing immunity,” which is an immune response that completely eliminates the organism from the pig, clears disease organisms such as Transmissible gastroenteritis from pigs.

Assumption #3: “Eventually, all animals in the population have the same immunity.” Even with diseases that stimulate strong, sterilizing immunity, subpopulations of naïve animals may remain if the disease organism is slow to move through the population.

In this regard, PRRS virus presents an additional challenge since original paradigms of PRRS as a fast-moving, blitzing infection of sow farms don't always hold true in field cases. This is especially true when new strains infect an endemic herd where the rate of transmission may be impacted by animals' partial immunity to a previously related strain of the virus. When diseases with slow rates of transmission or infection are encountered, the population must remain closed until well after all animals have been exposed.

Alternately, vaccination or planned exposure techniques can increase the rate of transmission in the herd.

Assumption #4: “As immunity stabilizes, there will be no host available in which the disease-causing organism can reside.” Rodents, feces, insects, farm pets and dirty equipment all represent potential reservoirs for disease organisms to safely hide for the next round of naïve pigs.

Survivability of swine pathogens in these areas is highly variable. It is critical that these potential reservoirs of disease are identified and eliminated.


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Illinois Producers Face Decision

Illinois producers face a big decision as to their future in the hog business, says University of Illinois Extension farm management specialist Dale Lattz.

This year is profitable, but predicting prices for the next five years is difficult, he says.

“The amount of continued expansion or liquidation, the strength of consumer demand for pork, the level of exports, and the availability of reasonably priced corn and protein supplements will largely determine the profitability of hog production during the next five years,” he states in the report entitled: “Costs to Produce Hogs in Illinois—2003.”

Illinois returns in 2003 averaged $38.15/cwt., compared to $32.25 in 2002. But total production costs in 2003 still exceeded returns by 78¢/cwt.

“For the five-year period, 1999 through 2003, total returns exceeded production costs by $1.01/cwt., says Laatz. “Three of the past five years show a positive return for farrow-to-finish enterprises.”

In 2003, feed costs were at their highest level since 1998, accounting for 60% of total costs, he says. Non-feed costs declined between 2002 and 2003.

Data came from members of the Illinois Farm Business Farm Management Association. In the study, farmers were divided into two categories: those farrowing fewer than 500 litters/year and those farrowing 500 or more litters/year.

Costs were higher for the smaller operations, which averaged $40.32 to produce 100 lb. of pork. Larger farms averaged $36.51/100 lb. “The most significant cost difference between the two groups of farms was in feed cost/100 lb. of pork produced,” says Laatz.

“Larger enterprises have a $3.38 lower feed cost than smaller ones – $21.37 compared to $24.75. The $38/ton lower price paid for commercial feeds by the larger enterprises and the 16 fewer pounds of feed it took to produce 100 lb. of pork accounted for the lower feed costs.”

“Producers should evaluate expected returns for more than one year before making new investments in hog production facilities,” says Laatz. “Over the past five years, returns for small producers averaged a negative 30 cents/100 lb. of pork produced and a positive $2.22 for the large producers.”

For the future, the key lesson for every hog producer is to pinpoint the level of production efficiency in his/her operation to realistically assess profit potential and staying power in the business, he states.

Use reasonable projections of input requirements and an efficiency level that can be maintained, especially when considering expanding or entering the hog business, stress Laatz.

Nutrient Management Training Course

The 2004 Comprehensive Nutrient Management Program (CNMP) Development Course is scheduled for Nov. 16-18 at the Radisson City Center in Indianapolis, IN.

Trainers educate technical service providers for producers who require CNMPs to obtain Environmental Quality Incentives Program funding.

Iowa State University, the University of Tennessee, Purdue University, Michigan State University and the University of Idaho in conjunction with USDA’s Natural Resource Conservation Service are providing training.

Information about the course, lodging and registration is available online at

North Carolina Market Study

Agricultural economists at North Carolina State University (NCSU) have received $465,000 to study different types of marketing arrangements in the hog and pork industries.

NCSU is part of a group of researchers headed by the Research Triangle Institute at Raleigh, NC, which received a $4.3 million contract from the Agriculture Department’s Grain Inspection Packers and Stockyards Administration to study livestock and meat marketing for hogs, cattle and sheep.

NCSU agricultural economists led by Tomislav Vukina will review numerous surveys, transaction data and conduct economic analyses to include:

  • Identifying and determining the use of emerging types of marketing arrangements such as production and marketing contracts;
  • Determining terms of the marketing arrangements and their availability to entities of different sizes and in different geographic locations; and
  • Determining the long-term implications of swine marketing arrangements on operating costs, animal and meat quality, marketing risks, livestock and meat prices and the structure of the livestock and meat packing industries.

Canadians Respond to Trade Cases

The Canadian Pork Council (CPC) has called on the U.S. pork industry to withdraw its trade cases against Canada, citing the U.S. Commerce Department’s Aug. 17 ruling that the Canadian swine industry farm support payments are fully in compliance with U.S. law and international trade rules.

The CPC release states: “Farm support payments are a fact of life in the U.S., Canada and the global agricultural industry. The result of the recent decision in this trade case is that the U.S. government has found that Canada continues to ‘do it right’ under U.S. law and the rules of international trade. Furthermore, payments made to Canadian farmers have not harmed the U.S. pork industry.”

While the Commerce Department found that federal income stabilization programs in Canada were not “illegal” based on preliminary results, the data did demonstrate that subsidies disproportionately benefited the hog industry, according to the National Pork Producers Council.

Worth County Ruling Upheld

The Iowa Supreme Court has upheld a ruling that the Worth County, IA, ordinance regulating livestock production is “void and unenforceable” because it violates state law that prohibits counties from regulating livestock operations.

The court noted that livestock production is to be expressly regulated by the state, says Eldon McAfee, legal counsel for the Iowa Pork Producers Association.

In 2001, Worth County enacted a county ordinance called the Rural Health and Family Farm Protection Ordinance. It set standards for toxic and odorous air emissions and worker safety and water pollution for confinement feeding operations. Agricultural groups challenged the ordinance, a district court agreed the statute was invalid and illegal, and the county appealed to the higher court.