Pathological lesions in swine at slaughter. IV. Pathological lesions in relation to rearing system and herd size.

Data from the meat inspection at a large regional abattoir in Norway was used to study the effect of different production systems and herd size on the occurrence of pathological lesions in pig carcasses. Three production systems were compared: combined production, production strictly in batches and continuous production. Only the former reared its own piglets. The data was collected in the period 1975–1977. The number of herds varied between 87 and 94, and between 26,000 and 30,000 bacon pigs were slaughtered each year. The herds were divided into three different size groups: ≤ 200, 201–400, and > 400 pigs slaughtered annually. Each year was considered separately. The study showed that the highest frequency of sound carcasses occurred in the combined production group. There was no significant difference between the two production groups rearing purchased piglets. Moreover, there was an inverse relationship between the frequency of sound carcasses and herd size, but the positive effect of the small herd was estimated to be less important than that of production system. The distribution of 16 different pathological lesions was also considered. Four lesions (pneumonia — moderate and severe —, pleurisy and scabies) were recorded at significantly different levels in the production systems all three years of recording. Analysis of the effect of herd size also showed that in the cases of moderate pneumonia and pleurisy, the small herds were at an advantage. The other lesions had a rather casual distribution among the groups. The statistical evaluation indicates however, that in cases of significant differences between the tested groups, only 20–40 % of the variation could be “explained” by our model comprizing production systems and herd size groups.