Relationships among seroconversion to Mycoplasma hyopneumoniae, lung lesions, and production parameters in pigs

Materials and methods—Forty-eight pigs from a 150-sow farrow-tofinish farm with a history of respiratory problems were weighed and bled every 2 weeks until slaughter. Serum samples were processed for serology to measure antibodies against M. hyopneumoniae, Actinobacillus pleuropneumoniae, and pseudorabies virus (Aujeszky’s disease). In addition, the thorax of each pig was radiographed every 2 weeks until slaughter. Lung parenchymal densities were determined from the radiographs and an average lifetime pneumonia (ALP) score was calculated. For each pig, radiographs were evaluated over time and used to determine when the pneumonia involved the highest percentage of the lung (pneumonic peak). Lungs were collected at slaughter and superficial lung lesions were measured. At the same time, pneumonic tissue was dissected and its relative volume was determined for each lung. For each weekly group of pigs, average daily gain (ADG) was calculated and correlated with pneumonic lesion measures (average lifetime pneumonia, volumetric pneumonia, and superficial pneumonia) for each pig as well as for each group. Onset of seroconversion to M. hyopneumoniae and A. pleuropneumoniae was tested for correlation with onset, extent, and severity of radiographic pneumonic lesions (ALP) and lung lesions seen at slaughter.