A study of associations between the salivary metabolite composition, pH, and gastric ulcers in lactating sows.

Abstract

Gastric ulcers are highly prevalent in the pig industry and are likely to cause discomfort or pain. However, there are no validated non-invasive methods to diagnose gastric ulcers in living pigs. Such diagnostics may help improve our understanding of gastric ulcers and promote control measures. Saliva protects the buccal mucosa and may play a role in the health of the pars oesophagea (located at the entrance of the stomach). Hence, changes in saliva characteristics could be linked to the occurrence of gastro-oesophageal ulcers. The aim of this feasibility study was to explore two tools that could help with gastric ulcer detection using non-invasive methods in the living pig: salivary metabolite composition and salivary pH. Twenty-six gilts and sows (hereafter sows) designated for culling due to repopulation management participated in this trial. Sows were followed through lactation until weaning to check their general health status. Sows were saliva-sampled prior to euthanasia, which occurred immediately after weaning (at 26 ± 1.5 days after farrowing, mean ± SD). To identify metabolites, global metabolomics and pathway enrichment analysis were performed on individual saliva samples. The salivary pH was measured. Stomachs were assessed postmortem, and stomach integrity was evaluated by assessing the pars oesophagea using two separate scoring systems: (1) a conventional scoring system that assesses the worst lesion present (overall stomach score) and (2) a scoring system that describes each type of lesion present in the pars oesophagea separately (lesion score). All sows had moderate to severe changes in the pars oesophagea, and 69.2% had at least one ulcer. The salivary pH was not related to stomach integrity. Metabolomic analysis identified metabolites that increased or decreased with changes in the pars oesophagea. The pathway enrichment analysis identified various metabolites as part of different metabolic pathways. L-histidine and lipoxin A4, which have been identified in saliva before and may be related to gastric ulceration, were detected. To conclude, this feasibility study identified a small number of salivary metabolites as potential biomarkers of gastric ulceration in lactating sows worthy of investigation in a larger, controlled study. However, the boxplots did not indicate changes in salivary pH with changes in the stomach integrity in these sows. Additionally, this study adds to the existing evidence of gastric ulcers in sows and suggests that it could be an important 'hidden' welfare problem.