RESUMO
The association between the extent of pathological lung lesions at slaughter and the time elapsed from seroconversion to slaughter was examined in a longitudinal study including 830 pigs from eight herds. Pigs from an age of 3 weeks were bled every fourth week, and the sera were analyzed for the presence of antibodies to Mycoplasma hyopneumoniae and Actinobacillus pleuropneumoniae serotypes 2, 5, 6, 7 and 12. At slaughter, the extent of mycoplasma-like catharral pneumonia, chronic pleuritis (dorso-caudal and ventro-cranial), interlobular-scar retractions, acute pleuropneumonia and chronic pleuropneumonia was recorded.Poisson regression was used to model the relationship between time elapsed from seroconversion to slaughter (divided into 4-week intervals) and extent of lesions, including "age at slaughter" and "gender" as independent variables and "litter" as an explanatory random variable. Analysis was only performed on lesions which had a prevalence >20% in at least five of the herds (mycoplasma-like catharral pneumonia, ventro-cranial and dorso-caudal pleuritis). Only a few consistent statistical associations were revealed across herds. Pigs seroconverting to M. hyopneumoniae close to slaughter expressed the largest extent of mycoplasma-like catharral pneumonia, and early seroconversion to M. hyopneumoniae was related to large ventro-cranial pleuritic lesions. In these eight herds, recording of the extent of pathological lung lesions at slaughter at most yielded insight into the within-herd epidemiologic dynamics of M. hyopneumoniae -- and not to any of the serotypes of A. pleuropneumoniae.
