Relationship to growth performance of pneumonia and atrophic rhinitis lesions detected in pigs at slaughter among four seasons

Abstract

Summary A commercial swine herd was selected for study, because pigs at slaughter repeatedly had lung lesions consistent with enzootic pneumonia and had snout lesions typical of atrophic rhinitis. Pigs born during various seasons of the year were allotted to 4 investigations and were evaluated from birth to slaughter. Individual lungs and snouts were identified and collected at the slaughter plant and later examined for gross lesions of bronchopneumonia and atrophic rhinitis, respectively. Each lesion was scored, and the following comparisons were made within investigations: prevalence and mean scores for lung lesions; prevalence and mean grades for snout lesions; correlations between lung lesion scores and growth indicators; correlations between snout lesion grades and growth indicators; and correlations between lung lesion scores and snout grade scores. Included in the growth indicators were average daily gain during the growing phase, average daily gain during the finishing phase, average daily gain during growing and finishing phases, and days to attain 104.5 kg of body weight. Prevalence of lung or snout lesions, mean values for lung lesion scores, mean values for snout lesion grades, and mean values for the various growth indicators were tested for statistical differences among the 4 investigations. Prevalence of lung lesions was highest (96%) for winter-slaughtered and lowest (81%) for autumn-slaughtered pigs. Mean scores for lung lesions were 7% (summer), 5% (autumn), 9% (winter), and 16% (spring). Prevalence of snout lesions was highest (85%) for spring-slaughtered pigs and lowest (42%) for autumn-slaughtered pigs. Mean grades for snout lesions were 1.5 (summer), 0.9 (autumn), 1.3 (winter), and 1.9 (spring). Pigs slaughtered in autumn had the lowest mean days to attain 104.5 kg (176 days), whereas pigs slaughtered in winter had the highest mean days to attain 104.5 kg (184 days). None of the correlation coefficients for growth indicators and scores for lung lesions were significant during any investigation. Only 2 significant correlations between growth indicators and snout grades were detected during any of the 4 investigations and those were observed for the winter investigation. Significant correlations were observed between grades for snout lesions and average daily gain-total (−0.37, P < 0.001), and between grades for snout lesions and days to attain 104.5 kg (0.40, P < 0.001). Results do not justify use of scores for lung or snout lesions evaluated in pigs at slaughter during any season to estimate reduction in growth rate or economic impact of pneumonia or atrophic rhinitis.