Effect of enzootic pneumonia of pigs on growth performance.

Growing pigs were naturally infected with a field strain of Mycoplasma hyopneumoniae to assess the effect of enzootic pneumonia on production. Both the initial ("breakdown") and endemic stages of infection were evaluated. The pigs were reared under environmental and management conditions commonly found on commercial piggeries in South Australia. Growth rate of pigs held in-contact with inoculated pigs was reduced by 12.7% (p less than 0.01) between 50 to 85 kg bodyweight. In the second trial inoculated gilts were used to naturally infect piglets during suckling. Growth rate of infected pigs was reduced by 15.9% (p less than 0.001) between 8 to 85 kg bodyweight, while feed conversion was depressed by 13.8% (p less than 0.05) between 10 to 25 kg bodyweight. At current feed and production costs this reduced performance added approximately $2.80 to the cost of every pig produced. These losses were recorded in groups of pigs in which enzootic pneumonia was present. At slaughter, 40% of lungs contained gross lesions of enzootic pneumonia which were free of significant secondary bacteria. The nature of the infection was established by gross and microscopic pathology and confirmed by the detection of specific complement fixing antibody in infected pigs and the demonstration of M. hyopneumoniae by direct immunofluorescent staining of lung sections.