TYPES OF FARM-MANAGEMENT AS RISK-FACTORS FOR SWINE RESPIRATORY-DISEASE

This study used the results of factor analysis described in a previous paper (D. Hurnik, I.R. Dohoo, A. Donald and N.P. Robinson, 1994. Fact or analysis of swine farm management practices on Prince Edward Island . Prev. Vet. Med., 20 (1994) 135-146) to describe the role of the farm environment in respiratory disease of swine. The factors (farm type d escriptions) were analysed using regression with prevalence estimates of enzootic pneumonia on 69 swine farms. Farms were dichotomized on en zootic pneumonia prevalence greater or less than 10%. Multiple logisti c regression analysis of the dichotomized data revealed that three far m types had an increased risk of having enzootic pneumonia. Multiple s ource feeder barns (farm Type 4) with low emphasis on disease entry an d control had an odds ratio of 2.38, meaning that farms closely matchi ng this farm type were over twice as likely to have enzootic pneumonia for every one unit increase in the factor score. Family farms using f loor feeding methods (Factor 5) had an odds ratio of 3.3 1, suggesting that this combination of management styles may be a contributing fact or in enzootic pneumonia. Integrated farms (Factor 6) had an odds rati o of 2.31 for having the condition, suggesting that larger farms that mill their own feed and are closer in proximity to other pig farms hav e a greater chance of having enzootic pneumonia. A linear regression o f the prevalence estimates of enzootic pneumonia on positive farms rev ealed that only farms with multiple source feeder barns and floor fed family farms were associated with a higher prevalence of enzootic pneu monia. Farms with extensive pig housing (Factor 1 ) were associated wi th a lower prevalence, suggesting that farms with ample pen space and air volume had fewer pigs with enzootic pneumonia. A similar analysis for pleuritis found a lower odds of lesions on farms with extensively housed pigs. This study confirmed that many commonly accepted risk fac tors, in combination, did indeed increase the likelihood of enzootic p neumonia. One previously unrecognized risk factor involved family farm s that tended to floor feed. Determining whether the individual variab les highly correlated with this factor are truly risk factors for enzo otic pneumonia requires more study. Factors affecting enzootic pneumon ia appeared to be different than those affecting pleuritis. Environmen tal influences are often discussed generally. This study indicates tha t the environment-disease interactions are different for the two disea ses.