There are several agents, both viral and bacterial, with the potential to cause disease within swine herds. It is important to discuss with your veterinarian which pose risks to your herd in order to develop an effective herd acclimation and stabilization program.

In the swine industry today, there are four diseases that no swine producer should live with — swine dysentery, atrophic rhinitis, sarcoptic mange and Actinobacillus pleuropneumonia (APP). If present, consider eradication vs. control and stabilization protocols. Each one of these has been successfully removed from a majority of swine farms in North America, so these will not be addressed further in this article.

Big Players

The two disease pathogens we spend the most time on from a herd stabilization standpoint are porcine reproductive and respiratory syndrome (PRRS) virus and Mycoplasmal pneumonia (MPS). Our goal for PRRS is to eliminate this virus from the breeding herd to prevent weaned pigs from carrying it into the nursery.

For Mycoplasma-positive herds, we want to minimize sow-to-piglet transmission in the farrowing crate in order to reduce overwhelming circulation in growing pigs.

For each disease, how this is done depends primarily on the desired health status of the sows and replacement gilts in the herd. Herds that maintain a positive-but-stable status for both of these pathogens are often producing young gilts (wean to feeder age) that are naïve for both pathogens, making it necessary to implement an exposure and recovery protocol.

For PRRS, this often involves exposure to field virus, PRRS vaccine or both. Acquiring gilt replacements at a young age allows for immunity to build and virus to be cleared well before entry into the sow herd.

With MPS, a similar approach is followed in gilt development, but it can be challenging to get natural exposure to this organism.

Sow herds in areas that are negative for PRRS and MPS don’t have to be acclimated for these diseases. Filtering sow breeding-gestation barns will change gilt development programs when these two pathogens are present.

Because air-filtering technology can stop the flow of these two pathogens into sow herds, it will become increasingly common to raise naïve gilts in geographical areas where there is reduced risk of lateral transmission of the pathogens. The air entering the gilt development unit may likewise be filtered, thereby eliminating the need to expose developing gilts.

Other Pathogens

There is more than just PRRS and MPS that we need to think about as part of a successful herd stabilization program. Streptococcus suis, Haemophilus parasuis, Actinobacillus suis, rotavirus and Escherichia coli also present health challenges. When putting together a plan to expose and stabilize gilts prior to entry into the sow herd, it is important to think about how each disease is transmitted.

For intestinal pathogens, exposure to feedback is often adequate. For pathogens that are taken up by the tonsil and respiratory tract, exposure to seeder pigs that are actively shedding the pathogens, is the most successful way to obtain active immunity.

A few pathogens that may need to be added to a herd acclimation and stabilization program are Mycoplasma hyorhinis/hyosynoviae and rotavirus types B and C. Neither has an effective vaccine available, and the best means to build active immunity prior to entering the sow herd is still being researched.

Enhancing Herd Stability

The first step in implementing strategies for stabilization and control is in knowing which disease challenges are costing your operation the most money.

The U.S. swine industry is fortunate to have great diagnostic tests to help in this process. Serology and molecular diagnostics (polymerase chain reaction or PCR) have become common tools to help understand swine disease profiles. Techniques like the sampling of oral fluids, as well as basic necropsies performed on farm, help pinpoint the disease challenges that exist within a herd.

Serology tests for antibodies to different diseases help determine what pigs are being exposed to. Cross-sectional serology and longitudinal serology are often used to profile a herd’s exposure to specific pathogens.

Cross-sectional blood testing is the sampling of a chosen number of pigs at different ages in a production system. The advantage to this method is it provides a relatively fast answer on immunity, but more interpretation is required. Cross-sectional testing of blood from several age groups can help determine when exposure occurred (Table 1).

Similarly, longitudinal bleeding of pigs involves a selected subset within a group that is followed throughout their life and tested for antibodies to determine exposure. This method requires less interpretation of the data, but it can take longer to get answers. Both methods help pinpoint when antibody levels increase, as well as when exposure occurs to better target vaccination prior to exposure.

Molecular diagnostics (PCR) tests for the presence of genetic material (RNA, DNA) of the bacteria or viruses. These tests tell us whether a pathogen is present in diagnostic samples and guides us closer to knowing the time of exposure.

PRRS, MPS, porcine circovirus type 2 (PCV2) and Lawsonia intracellularis (ileitis) are pathogens that we routinely test for antibody response by serology and exposure with PCR.

Developing Health Stability

Health stability is a new catchphrase in disease management. Commonly a goal for all phases of production, stability implies a reduction in the concentration of, or, in some cases, the complete elimination of certain swine pathogens in a population. Gaining herd health stability reduces the transmission of disease agents, leading to decreased challenges throughout all phases of production.

There are several ways to develop health stability in populations of pigs:

  • Avoid mixing weaned pigs from multiple sow farms.
  • Employ strict sanitation measures to reduce direct exposure to potential disease-causing organisms.
  • Apply all-in, all-out pig flow, wash and disinfect to ensure that any disease concerns are not passed onto incoming groups.

These steps, together with the building of active immunity through vaccination, are some of the most effective ways to reduce health challenges in pigs. Additionally, antimicrobial treatment programs are implemented to lower bacterial shedding, thereby reducing spread in groups.

Rope Testing

One difficulty with mass testing within a population is obtaining a consistent sample that can accurately represents what pigs are being exposed to. Oral fluid testing, placing cotton ropes in pens for pigs to chew on, collects fluids for testing. This is a fast and easy way to get an idea of when pigs are exposed to pathogens.

Currently, rope testing experiments are being conducted for PRRS, PCV2, swine influenza virus, Haemophilus parasuis, Strep suis and Actinobacillus suis.

Routine Necropsy

Posting pigs and submitting samples is an efficient way to identify the most costly diseases in your herd and the causes of mortalities or decreased performance. The key to the success of necropsies is to do them routinely to accurately diagnose the problem, while providing a good tool for disease profiling. Necropsy investigations of many pigs when mortalities are high in nurseries or finishing barns can help pinpoint weaknesses.

Figure 1 shows peak mortality in multiple groups of finishing pigs at three to six weeks post-placement. Graphing mortality by the week on feed helps pinpoint when mortalities are occurring, when to submit tissue for diagnostics, and when to start intervention strategies.

Necropsy and tissue samples submitted from untreated animals provide the best results. Table 2 shows symptoms of pigs and the best testing methods to use for those symptoms.
Slaughter checks can be a useful tool for monitoring progress of intervention strategies, or to determine the pathogens affecting pigs at marketing, such as ileitis, MPS, PRRS or bacterial septicemias.

Possible Interventions

  • PRRS testing by 8 weeks of age tells if the virus has circulated through the group. Possible interventions may be to vaccinate weaned pigs with PRRS ATP or MLV (Boehringer Ingelheim Vetmedica, Inc.). Test for PRRS stability at the sow farm to verify no virus leakage. With no intervention, this could cost the producer $10-15/pig.
  • Ileitis testing by 12-16 weeks of age tells if there is exposure to Lawsonia occurring and by 20 weeks of age if it has moved through the group. Potential interventions may be to vaccinate six weeks prior to exposure at 10 weeks of age with a Lawsonia intracellularis vaccine or implement an in-feed antibiotic control program in finishing diets. With no intervention, the potential cost to the producer may be $7-10/pig.
  • PCV2 testing by 4 weeks of age tells if PCV2 is circulating within the group and if there is a high level of virus present within the finishing group. Possible interventions may be to test for sow farm stability by sampling blood of piglets prior to colostrum intake for PCV2 virus, review vaccination timing and program to ensure pigs are getting vaccinated prior to exposure to PCV2. The potential cost to the producer without intervention could be $0.63-$3/pig.

Submitting Samples

With all the work that goes into collecting samples, it is important to get them shipped safely to the diagnostic lab. Next-day delivery is essential, especially in warm months, to ensure the sample received is fresh. Samples, especially intestines, start breaking down within minutes to hours without chilling or addition of formalin. Package samples on at least three frozen ice packs to be shipped for next-day delivery.

Choose a diagnostic lab that will run the correct tests and get the right answers. Important considerations include:

  • Utilize a diagnostic lab that specializes in swine pathology and has at least one swine pathologist.
  • Ensure your veterinarian has a line of communication open with the swine pathologist.
  • Ensure the lab can test for the disease you are looking for and have the “gold standard” test available.
  • Ensure the lab is capable of receiving next-day delivery and expediting testing when needed.

The Midwest has many diagnostic labs to choose from. The University of Minnesota, Iowa State University and South Dakota State University are proficient labs used.

Diagnostic labs play a key role in determining the disease profile at a reasonable cost. For example, a necropsy investigation at the University of Minnesota Veterinary Diagnostic Laboratory costs a producer about $120, but the testing that is done to work up a respiratory or diarrhea case can cost the diagnostic lab several hundreds to thousands of dollars above that cost. The labs provide a battery of tests not available in the private sector with an unbiased evaluation. The ultimate goal of investigating and monitoring disease in food animals is to provide a healthy pig for the food supply.

Focus on Replacement Gilts

Nowhere is herd health stability more paramount than the breeding herd. When a breeding herd becomes unstable for any number of pathogens, there is often excess vertical transmission in the farrowing crate from sow to piglet. Piglets that are subject to overwhelming challenge prior to weaning have a reduced ability to respond to vaccination, fail to perform to their genetic potential, and succumb to disease at higher rates than health-stable herds.

From an immunity standpoint, the breeding herd is a dynamic population. Farms routinely remove aging animals and bring in younger replacements in order to capture the greatest production. As older parity sows exit the herd, so exits the immunity of several parities’ worth of vaccination and environmental exposure. Those sows are replaced with gilts that are often immunogenically naïve to several herd pathogens.

An example of this difference in immunity is the parity segregation system where offspring from sows vs. gilts have very stable health. Gilts become a necessary breeding tool, and a breeding herd will never achieve desired health stability without developing a proper gilt immunity program. Producers should avoid changing their gilt source once an effective stabilization program is attained, as new sources will often destabilize sow herd and growing pig health.

The most successful gilt development programs:
1. Obtain a young gilt (weaned to feeder age), which allows as much time as possible for vaccination and exposure/recovery to common herd pathogens.

For several swine diseases, we want exposure (infection) to occur in growing gilts to ensure an active immune response is built and disease agent is cleared before entry into the sow herd.

Internal multiplication and production of gilts can work well, as long as the herd’s genetic improvement program does not suffer.
2. Use commercially available or autogenous vaccine and immunize often. Gilts are a valuable piece of the operation and can receive multiple vaccinations for specific disease concerns within that herd. Gilt vaccination later in development for circovirus, SIV and MPS has become increasingly common due to health instability these pathogens have presented in herds. Also, vaccination for ileitis, salmonella, parvovirus, leptospira and erysipelas should be a part of a complete gilt entry program.
3. Acclimate gilts frequently during development with material from the sow farm they are destined for.

This is often an underutilized practice that has a lot of value in generating herd-specific immunity. Putting together a thorough acclimation program may involve:

  • Introduction of cull gilts from the sow farm (younger gilts from the sow herd that have the best chance of shedding into the gilt developer; younger culls preferred).
  • Sending off-quality, weaned pigs to commingle with gilts.
  • Creating feedback material at the sow farm that is easy to manage so that it can be routinely provided to gilts.

For PRRS, live-virus exposure to gilts early in development ensures they have been exposed to the most recent herd virus and will develop immunity to this virus prior to arrival in the herd.

Several areas within the breeding herd affect how immunity is built and how health stability is maintained. Within the breeding and gestation herd, a prefarrowing vaccination program elicits immunity to common pathogens, ensuring that when these pathogen levels rise, herd immunity can naturally and rapidly knock those pathogens back down.

As discussed, feedback practices are also a valuable addition to vaccine, helping stimulate a more customized or herd-specific immunity to the pathogens that exist on a farm (see sidebar above).

Focus on Farrowing

By the time a sow enters the farrowing house, her immunity has been built for that farrowing. In the farrowing house, health stability is now influenced by the practices employed by farm staff. All-in, all-out flow of sows in farrowing rooms with strict cleaning and disinfection give us a clean slate to start from a disease stability standpoint.

Once farrowing starts, the immunity-rich colostrum is the biggest driver to successfully maintain stability. All neonatal pigs need to nurse colostrum in the first 6-10 hours or they will become health challenged and struggle to survive. In our experience, farms that place observant caretakers with a primary focus of starting every pig in the first hours after birth have the greatest survivability and highest-quality pigs at weaning. Low-viability pigs or those that are unable to receive colostrum should be humanely euthanized.

After Day 1, additional drivers of farrowing house health stability are related to movement and holding back of pigs. Mixing pigs creates instability. Mixing a few poor pigs that are shedding pathogens at an increased rate with good pigs will create entire litters that become disease challenged. Similarly, holding pigs back at weaning, especially during times of disease challenge, maintain pathogen levels in a farrowing house, making it increasingly difficult to break the disease cycle. Remove these pigs from the sow farm or euthanize them to reduce disease transmission.

Feedback Provides Excellent Protection

Feedback protocols are such an important part of a herd immunity program, especially for generating maternal immunity against several pathogens that cause scouring in neonatal pigs. Although there isn’t a wealth of science behind the practice of feedback, observational data from several farms show a dramatic reduction in the incidence of scouring litters from those groups having received feedback in farrow and nurse litters. Three areas are quite important:
1. Use only fresh feedback material. Bacteria can produce toxin rather quickly (several hours), and some pathogens can break down over extended periods, altering their immunogenic properties. Mix and use feedback material on the same day.
2. Get feedback to bred animals multiple times prior to farrowing, and allow enough time for shedding to cease before those groups enter the farrowing house. Feeding back six, five and four weeks pre-farrow with each sow receiving multiple doses each week is a common practice.
3. Test feedback material so that you know what is there. It’s difficult to get protection against a type C rotavirus if it isn’t contained in the feedback material. Simple diagnostic testing on feedback samples can answer what the product contains. A feedback containing desired pathogens can be made in large quantity, frozen in a convenient size until contents are confirmed. These frozen stockpiles of feedback can then be used for weekly feedback processes to increase anti-scour immunity in groups prior to farrowing.