Differential expression of microRNAs in the prefrontal cortex as indicators of sheep welfare

Indicators that are used to assess animal welfare tend to be non-specific and provide limited information on how a situation is experienced by an animal. There is growing evidence that microRNAs could be useful biomarkers of brain function and experience in humans, however, there has been limited work evaluating their use for assessing experience, and thus the welfare of animals. In this study, we evaluated microRNAs as indicators of changes in the welfare state of sheep. We induced differences in the experience and coping capacity of 34 female Merino sheep in response to a psychological challenge of isolation at the start and end of a period of three dietary manipulation treatments. The first group was fed to maintain liveweight constant during the three periods (n = 11); the second group was fed to increase liveweight in period 1, keep liveweight constant in period 2, and decrease liveweight in period 3 (n = 12); and the third group was fed to decrease liveweight in period 1, keep liveweight constant in period 2, and increase liveweight in period 3 (n = 11). Next generation sequencing identified seven mature miRNAs that were differently expressed between the sheep that were fed below their maintenance requirements and those that were fed at maintenance. The sheep that were fed below their maintenance requirements had an increase in the expression of oar-miR-329a-3p, oar-miR-329b-3p, and oar-miR-485-5p, and a decrease in the expression of oar-miR-106b, oar-miR-1185-5p, oar-miR-21, and oar-miR-26b compared to the sheep that were fed at maintenance. These differentially expressed microRNA from the dorsolateral prefrontal cortex were enriched in pathways that are associated with gene expression, intracellular signalling, and neuronal processes, which could provide insight into the mechanisms of metabolism, and possibly the welfare state of sheep. Further research is needed to validate the differently expressed miRNA as indicators of welfare given the lack of difference in expression levels between the sheep fed above and below their maintenance requirements.