Enzootic pneumonia of pigs in South Australia--factors relating to incidence of disease.

Environmental and management conditions of 15 herds with a high-prevalence (greater than 70%) of enzootic pneumonia of pigs at slaughter were compared with 16 herds with a low-prevalence (less than 30%) to determine factors commonly predisposing pigs to enzootic pneumonia in South Australia. Comparisons were made of herds having greater than 100 sows (fully intensive units) and also small herds having 20 to 70 sows (sideline units). Half the herds were visited in summer and half in winter to detect seasonal factors. In small herds, factors commonly found associated with a high prevalence of enzootic pneumonia were larger numbers of pigs per shed section (p less than 0.001), larger group sizes (p less than 0.01) and draughty farrowing and weaner accommodation (p less than 0.01). In large herds, factors associated with a high prevalence were higher pen stocking rate (p less than 0.05) and airspace stocking rate (p greater than 0.05), and a trend toward higher atmospheric ammonia levels in summer (p less than 0.1).