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Though problems of respiratory disease continue to plague swine producers, the causative agents have some old and familiar names: PRRS virus, Swine Influenza, and Mycoplasma hyopneumoniae. Other common culprits like Haemophilus parasuis (Hps) and Pasteurella multocida can complicate pneumonia. Hps can be a severe problem on its own.

Common features

These three pathogens all have one thing in common; they are not bacteria. Both PRRS and SIV are viruses. Mycoplasmas are somewhere between a virus and bacteria, and are some of the smallest free living organisms. They affect either the immunity of the lung, damage the airways, or both.

Aerosol spread of these agents may occur, for many miles in the case of Mycoplasma. Cool, humid conditions may help spread disease between farms on air currents, which will “flow” along terrain similar to how water runs off. Placing barns to limit exposure to these “heavy” air currents may reduce risk of infection.

Sorting out the mess

Growth limitation is the problem resulting from poor respiratory health. When healthy pigs fail to grow to their potential or are lost as dead and unmarketable pigs, revenues go down and costs go up. Identification of the responsible agents is critical to select and place control measures.

Serology can help you understand the pathogens present and when they are affecting pigs. Cross sectional studies look at pigs at a single time, bleeding several different age groups at once. (See the June 2001 issue of Insight for more details). Serial bleeding formats follow groups of pigs over time. These may provide more precise information about pathogen exposure, but take longer to complete. Ask your veterinarian about the benefits of a routine serology measurement program.

Slaughter checks can also be used to assess the health of a pig herd. Unfortunately, estimating the economic impact of health is difficult from slaughter checks. The best measure to assess the cost of poor respiratory health is the percent of pigs with any type of lung lesion present (the percent of pigs with pneumonia damage to the lung). The average percent of pneumonia (average lung score) may be misleading when pigs have been infected just before harvest.

Reconnaissance leads to plan

Begin by evaluating the percent of pigs in several groups to see how many have lung lesions. If none are detected, great job! Respiratory health is excellent. For most herds though, pigs with lung lesions will be found. Record the percent with damage and keep this for comparing to later evaluations.

Measure serology in multiple groups to determine which agents are present, and when they are striking. The impact of infecting pigs with pathogens, indicated by positive serology, can be evaluated using peer-reviewed studies. PRRS virus and Mycoplasma hyopneumoniae positive pigs grew about 0.10 #/day less than negative pigs…in a 120 day flow, that's up to 12# a pig lost due to each disease agent! SIV infection had less than half that impact on growth rate.

Gathering the necessary information is the first step to improving health. Reducing the negative impact of poor respiratory health on pigs helps maximize your financial health!

More information

Schwartz KJ. Common Infectious Agents: Diagnostic Laboratory Perspective. Proc Iowa State Swine Dis Conf 2001. Pp7-23.

Yeager MJ. The diagnostic sensitivity of immunohistochemistry for the detection of porcine reproductive and respiratory syndrome virus in the lung of vaccinated and unvaccinated swine. J Vet Diagn Invest 14:15-19 (2002).

Regula G, et al. Comparison of serologic testing and slaughter evaluation for assessing the effects of subclinical infection on growth in pigs. JAVMA 2000; 217 (6):888-895.