A study of adventitious bursitis of the hock of the pig

Abstract

A review of the literature showed that adventitious bursitis was recognised in most European countries with large pig populations. On the whole, there was agreement that hard floors without bedding played a significant role in the pathogenesis of the disorder.

An abattoir study was conducted in five Scottish abattoirs in order to establish the prevalence and severity of adventitious bursitis in finished pigs. Data were collected from 14,046 pigs of which 7,350 were male and 6,696 female. Adventitious bursitis of the hock was noted in 12,220 pigs (87%) and the mean severity score was 1.598 (score range 0-4). Bursitis was present on the left leg of 11,579 pigs (82.436%) and in the right leg of 11,558 pigs (82.286%). The prevalence of bursitis in males and females was 87% and 86% respectively. The prevalence of bursitis in winter (87.5%) was higher than in summer (84.5%) while the severity score in winter (1.65) was also higher than in summer (1.47). Adventitious bursae on the hock were found on three aspects: plantar, lateroplantar or medial. When bursitis was present it was usually bilateral and in every case the bursae were present subcutaneously over the plantar aspect of the lower calcaneous, or the lateroplantar aspect of the lower calcaneous or the promontory of the central tarsal bone. A histopathological study suggested that bursae arise as a result of pressure trauma on lymphatic vessels and capillaries which resulted in the exudation of fluid and fibrin. This fluid filled sac became walled off by fibroblasts.

Adventitious bursae were also noted on the forelegs and over the points of the hocks (capped hock). The prevalence of capped hock in males (3.58%) was higher than in females (1.97%) and when capped hock was present, bursae on other aspects of the hock were either small in size or completely absent.

It was shown that infection played no role in the pathogenesis of the lesions.

A farm housing survey showed that there was an association between pigs with bursitis and rearing on hard floors. Further studies on pigs from birth to slaughter, indicated that bursitis developed early in life (< 3 weeks of age) but only did so when the floors were hard, with the prevalence and severity of bursitis being highest on concrete slats. Deep bedding not only prevented bursitis but also reduced the prevalence and severity of bursae already present.

It was also shown that the degree of bursitis increased on the Straw-Flow system which was developed mainly for welfare reasons. There was a good correlation between the prevalence of foot-rot lesions and the severity of bursitis. Concrete with a rough abrasive surface caused a high prevalence of foot-rot lesions and a high frequency of bursae with erosions.

Data from one herd with a bursitis problem showed that bursitis was moderately heritable, i.e. about 25% of the variation in severity was genetic in origin. Other important determinants included the depth of subcutaneous fat, breed and skin thickness.

The main economic impact was due to the weight of tissue condemned and the number of breeding stock rejected for breeding purposes. Bursitis cost the Scottish pig industry about £406,000 in 1991.

A high prevalence and severity of bursitis might indicate a welfare problem but a modest degree of this 'blemish' was thought to be acceptable as there were good reasons for supporting the housing systems involved.