Respiratory disease in the finishing stage of production is a challenge for both producers and swine veterinarians, and the complexity of managing these diseases has increased due to interaction of the agents in this stage of production. Common agents include: swine influenza (SIV), porcine respiratory reproductive syndrome (PRRS), porcine circovirus type 2 (PCV2), mycoplasma, Actinobacillus suis, Actinobacillus pleuropneumonia, Pasteurella multocida and other bacterial agents. Viral agents seem to be the biggest problems to control.

There is debate over which agents require vaccination and when these vaccinations should be administered for optimal control. Environmental control and making sure there is minimal additional stress to pigs are other factors that contribute to the problem.

It is not specifically understood why these viral agents are more challenging than in the past but one of the biggest changes in US production systems is the transition to multi-site production systems, and in some cases, multi-sourcing as well. This has resulted in more movement of pigs from different sources in a small geographical area.

Diagnostics

Identifying the pathogens at work in the herd or flow of pigs is the first step to control. Many tools are available to evaluate these herds and flows today. Obtain information on the source of pigs and the history of the originating farms. Work with your veterinarian to understanding the clinical presentation to determine the best diagnostic plan. Post mortems are still the best source of information from infected groups, or just prior to the time that breaks typically occur. Routine post mortems can be helpful in determining the cause of the problem. Have your veterinarian train your farm staff and field supervisors to perform post mortems on a timely basis and teach the proper method of collecting tissues so the material is not compromised. The use of digital cameras by farm workers and field supervisors can be beneficial in determining the cause and severity of problems in the herd or flow.

Serology can be used to determine the presence of an agent and the timing of infection. In addition, the use of temperature loggers is a good way to see what is happening in the barns.

Records can be helpful in determining the time of the problem such as the mortality by weeks on feed that can be generated by various programs. The data can be sorted many different ways to help better define the problem. For example the flows can be sorted to see if problems vary by flow or source of pigs. They can also break down the sites by geographic area as well as single stock versus double stock, nursery to finish versus wean to finish etc. These closeout records are the best tools to help define the cost and potential losses. The backbone to an effective control program is to have a good diagnostics plan. Once the diagnostics are done, proper control procedures can be put in place.

Specific Agents and Conditions

Swine Influenza Virus (SIV)

SIV is certainly a major player among grow-finish respiratory diseases. Its ability to continually change through both genetic shift and drift has made this an even more complex agent to control. One of the biggest challenges has been shedding from sow herds and early signs of respiratory disease in the nursery or wean-to-finish production phases.

The best diagnostic for SIV is to identify pigs with a fever (>104 degrees) and take nasal swabs for culture. Vaccination at this time is the only intervention and many herds have gone to autogenous (farm-specific) products because of the changes in the virus versus the present vaccines available. Vaccination pre-farrowing has been an effective means of controlling these problems once the right strains are in the vaccine. Area spread in pig-dense areas is an additional means of spread. Vaccination in the finishing phase has been a challenge due to the maternal antibody interference with the vaccine, and some pigs break with the disease before the group can be vaccinated. Currently, acute outbreaks in the finishing phase are treated with aspirin to control fever and keep the pigs eating so fewer gastric ulcers develop from loss of intake. Antibiotics are used following the aspirin in the water to avoid secondary bacterial infections. The common choice is tetracycline but treatment depends on the pathogen profile and experience in the herd or system.

Porcine Circovirus Type 2 (PCV2)

PCV2 has added a level of complexity to this problem. PCV2 vaccination has become more widely available and has proven to be very effective in improving mortality and growth and performance. Many trials are still in process, however, to evaluate the proper timing of vaccinations and dosage levels. The answers may not be the same for every herd and researchers will need to evaluate the effect of having sow herds vaccinated and replacement gilts entering the herd that have been vaccinated at a young age.

Porcine Reproductive and Respiratory Syndrome (PRRS)

PRRS is still a problem in grow-finish pigs, partly due to the number of different strains circulating in the swine population. Generating negative pigs from the sow farm is the best control. One of the challenges is when negative pigs flow into areas with infected herds and there is aerosol cross contamination. Vaccination can be done with current modified live virus (MLV) vaccinates with pigs being vaccinated at the time they enter the site. One of the best control measures is to make sure you practice good biosecurity: Changing coveralls and boots before going into finishing sites (Danish entry system) has been an effective control as well as isolating incoming products.

Mycoplasma

Mycoplasma continues to be a challenge, and we wonder if new and different strains are making this a bigger problem. Due to the difficulty of growing mycoplasma cultures, it is hard to know if this is true or not. The industry needs new tools to help answer these questions. Vaccination has moved to the farrowing phase, with most pigs being vaccinated at processing and weaning. In herds that continue to have problems even with good vaccination programs, the use of pulse dosing of antibiotics has been helpful to get the desired control. Herds and production flows are using eradication projects to eliminate mycoplasma (or at least the clinical effects of mycoplasma) so they will have a negative downstream flow.

Actinobacillus

Actinobacillus suis is a more recent concern in the grow-finish phase. It can be quite severe, with sudden deaths occurring throughout finishing but primarily in the early finishing phase. Presently, there are no commercial vaccines, but the autogenous products seem to be helpful in controlling this disease. Medication is also helpful for A. suis.

Actinobacillus pleuropneumonia is less of a concern than it once was, since most herds have depopulated and eliminated the disease. New strains are being identified and some are less pathogenic than type 1 and 5. There is a new serologic test that can test for all strains (Idexx APP APXIV test) and several new antibiotics that are helpful in treating APP, but they can be expensive.

More to Learn

At this time it feels like the viruses are winning. There is still much to be learned about the various interactions of pathogens. As an industry, we may be better off trying to eliminate or eradicate some agents so they do not complicate the disease profile on farms.

Pig flow may be one of the most important ways to manage these problems. If there are problem herds in commingled flows they will need to be flowed with other like herds or separately. Having a monitoring system to identify problem herds quickly is especially important in these commingled flows.

Environmental control is also critical to avoid stress that can set up and make these conditions worse. The new controllers available in many buildings today can do sophisticated things but unless they are used properly, they can result in additional problems with the pig's environment. Evaluate the system to make sure it is setup and functioning properly. Many farms and systems are using 'standard operating procedure' to make sure the barn temperature is set properly.

Using good diagnostics and defining the problem will help us to break down and solve these complex problems. Every herd and flow will have to find its own solution to challenges because there is not just one solution. Veterinarians and producers will have to remain creative so they can continue to adapt to changes in disease presentation.

Dr Paul Yeske is a veterinarian with the Swine Vet Center in St. Peter, Minnesota. He presented a paper on which this article is based at the 2008 American Association of Swine Veterinarians meeting.

October 2008

Further Reading

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Find out more information on PRRS by clicking here.

Further Reading

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Find out more information on SIV by clicking here.