Exploring the hidden welfare problem of gastric ulceration in sows: behaviour and saliva composition as possible methods of diagnosis

Gastric ulcers are highly prevalent in the pig industry and evidence suggests probably affect pigs in all productive stages. Gastric ulcers affect pig welfare as they cause some degree of discomfort or pain (observed by a change in behaviour) as well as impacting performance. Gastric ulceration is a hidden problem as it is difficult to identify in living pigs and there is no method of diagnosis that is both non-invasive and affordable. In this thesis, I hypothesised that re-directed oral behaviours (e.g. sham chewing, biting bars) and changes in saliva characteristics may be of use for the diagnosis of gastric ulceration in pigs. Re-directed oral behaviours have been largely related with chronic hunger in sows which appear as a way to cope with a diet and environment that does not fulfil sows’ nutritional and behavioural needs. However, these behaviours have also been observed in finishing pigs as well as in gilts and sows fed ad libitum. Furthermore, there is some evidence that the behaviour of finishing pigs changes with the presence of gastric ulcers. Saliva composition has been reported to change with various illnesses or conditions but also, recently, with the presence of gastric ulcers in finishing pigs. Chapter 2 describes oral behaviours present in finishing pigs and compares them to the behaviour of sows. All oral behaviours studied were observed in finishing pigs, and the rate was the same as compared to sows. The behaviours which were least frequent and performed by the least number of animals in both finishing pigs and gestating sows were self-directed oral behaviours. Self-directed oral behaviours are much more difficult to explain in finishing pigs as opposed to oral behaviours that involve the interaction with an object or conspecific. Chapter 3 explored the relationship between self-directed oral behaviours (chewing movements, wind sucking, tongue playing and jaw stretching) and the presence of gastric ulcers in finishing pigs. All self-directed oral behaviours, but jaw stretching, were observed in both pigs with healthy and ulcerated stomachs (video observations). All observed behaviours were the same between both groups. Chapter 4 explores the relationship between re-directed oral behaviours (live observations) as well as salivary composition and pH with gastric ulceration in gestating and lactating sows. All sows were found to have some level of ulceration and the prevalence of gastric ulcers was 67.57%. The rate of re-directed oral behaviours was not affected by overall stomach score or lesion score during either gestation or lactation. Salivary pH was not affected by stomach integrity. Saliva composition changed with the overall stomach score and lesion score in gestating and lactating sows. Lipoxin A4, Succinic acid and L-Histidine were identified as possible biomarkers of gastric ulceration. Chapter 5 is a systematic literature review of the variation of re-directed oral behaviours according to housing system, diet and feeding practices, and environmental enrichment in gestating gilts and sows. All of the results of the included studies can be explained by ‘chronic hunger’ theory or their housing environment. Although the design of these studies was to test factors which relate to hunger and re-directed foraging, rather than the health of the upper digestive system. This thesis shows that oral behaviours do not have a clear link with gastric ulceration in finishing pigs, or in gestating and lactating sows. However, oral behaviours were observed in finishing pigs and some of these remain unexplained (e.g. self-directed oral behaviours). Also, all re-directed oral behaviours in gestating gilts and sows can be explained by chronic hunger or housing environment as shown by the systematic literature review. Possibly, the remaining unexplained oral behaviours may be a response to an environment that is still insufficient for the pig to fulfill its behavioural needs and/or other conditions affecting the upper digestive system. Saliva composition is linked to gastric ulceration in gestating and lactating sows, and possible biomarkers were identified in this thesis. More studies are needed to identify and validate biomarkers for gastric ulceration in pigs.