Types of farm management as risk factors for swine respiratory disease

Abstract

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. Factor 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 descriptions) were analysed using regression with prevalence estimates of enzootic pneumonia on 69 swine farms. Farms were dichotomized on enzootic pneumonia prevalence greater or less than 10%. Multiple logistic regression analysis of the dichotomized data revealed that three farm types had an increased risk of having enzootic pneumonia. Multiple source feeder barns (farm Type 4) with low emphasis on disease entry and control had an odds ratio of 2.38, meaning that farms closely matching this farm type were over twice as likely to have enzootic pneumonia for every one unit increase in the factor score. Family farms using floor feeding methods (Factor 5) had an odds ratio of 3.31, suggesting that this combination of management styles may be a contributing factor in enzootic pneumonia. Integrated farms (Factor 6) had an odds ratio 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 have a greater chance of having enzootic pneumonia. A linear regression of the prevalence estimates of enzootic pneumonia on positive farms revealed that only farms with multiple source feeder barns and floor fed family farms were associated with a higher prevalence of enzootic pneumonia. Farms with extensive pig housing (Factor 1) were associated with 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 factors, in combination, did indeed increase the likelihood of enzootic pneumonia. One previously unrecognized risk factor involved family farms that tended to floor feed. Determining whether the individual variables highly correlated with this factor are truly risk factors for enzootic pneumonia requires more study. Factors affecting enzootic pneumonia appeared to be different than those affecting pleuritis. Environmental influences are often discussed generally. This study indicates that the environment-disease interactions are different for the two diseases.