Wildlife feeding activities induce papillae proliferation in the rumen of fallow deer

Wildlife feeding activities are growing as a trend in recent years, with wild ruminants (e.g. deer in urban parks) receiving an increasingly unnatural diet as a result of public attention. The effects of diet on the gastrointestinal tract of ruminants have been established in the context of animal agriculture, with highly modified diets driving morphological changes in the rumen papillae. However, these dietary effects have not been widely explored in wild ruminants that are exposed to recreational feeding. The aim of this study was to investigate the effects of human-wildlife feeding interactions on the rumen papillae of a wild population of fallow deer in Phoenix Park, Dublin. The length, width, and density of the ventral rumen papillae were compared across a variety of feeding behaviours, ranging from deer that consistently accept food from humans to deer that rarely, if ever, accept food from humans. The surface enlargement factor (SEF) was also calculated as a measure of overall absorptive surface in the rumen and was similarly compared. Statistical analysis revealed that consistent acceptors of food had significantly higher papillae density than those that do not accept food. Increased papillae density in deer receiving high amounts of human food suggests a shift in the internal rumen environment. A lack of significant change in the SEF suggests that a cellular change may be occurring. This artificial rumen state requires further attention to elucidate the full extent of these feeding impacts on the gastrointestinal integrity of these wild deer. Moreover, this is a call for research into other human-wildlife feeding interactions that occur in human-dominated landscapes, beyond the deer of Phoenix Park.