The urea nitrogen salvaging process (UNS) supports the symbiotic relationship between ruminants and their gastrointestinal microbiome by both supplying nitrogen and buffering bacterially-derived short chain fatty acids (SCFAs). Studying such physiological processes via investigation of rumen papillae morphology and functioning, as well as western blotting to detect rumen urea transporters, allows researchers to test hypotheses linking physiology and ecology. The goal of this innovative approach is to indicate the way forward for future research. Our previous studies have shown the importance of the UT-B2 urea transporters in the rumen of wild fallow deer living in Phoenix Park, Dublin. In this current pilot study, we investigated the effects on these transporters of seasonal changes – linked to changes in feeding intake during and after the mating season - and acceptance of artificial food from park visitors in adult male bucks. Investigation of the rumen papillae revealed that animals culled in January had significantly longer papillae than those culled just after the rutting season in November, when bucks interrupted feeding from a few days to weeks. In contrast, western blotting analysis showed that there was no significant difference in the abundance of UT-B2 transporters between these two groups. Adult males that had displayed consistent begging behaviour to obtain food from human visitors to the park had a higher papillae density. Furthermore, these animals had a significantly higher abundance of UT-B2 transporters, which was shown by immunolocalization studies to be predominantly in the stratum basale layer of the rumen papillae. Our research suggests that human-wildlife feeding interactions can have subtle effects on the physiology of individual animals involved. The findings of this novel study therefore improve our understanding of basic rumen physiological processes, but also add insight into the unseen effects that humans feeding wildlife may have.
