Pathogenesis and pathology of shoulder ulcerations in sows with special reference to peripheral nerves and behavioural responses to palpation

Shoulder ulcerations are common in breeding sows in production systems but the consequences for the animals in terms of pain or discomfort are not well-described. This study presents data from a histopathological examination of shoulders of sows, specially focusing on the peripheral nerves in the region and the behavioural responses towards palpation of animals with traumatic neuromas but without ulcers. The study included 155 sows from seven Danish herds initially screened and stratified according to absence/presence and size of shoulder ulcers 3-4 weeks post-partum, out of which 71 were free of ulcerations and 84 had different stages of ulceration. Before collection, sows were subjected to shoulder palpation and behavioural responses were registered. From the consecutive pattern of development of ulcerations it is evident that shoulder ulcerations develop from top-to-bottom.A high frequency of traumatic neuromas was found in both healed and unhealed lesions. The observation of viable nerve-ends in shoulder ulcerations makes it likely that ulcerations are associated with pain. Moreover, the presence of traumatic neuromas in healed ulcerations indicates that there is discomfort even after the lesions have healed. This is further supported by the behavioural finding that rubbing behaviour in response to palpation was increased on the day of sample collection of the shoulders in sows with traumatic neuromas but without shoulder ulcers (P = 0.053). Further studies are needed for final confirmation but these results suggest that shoulder ulcers may be associated with pain even after healing.