Cardiac activity in dairy goats whilst feeding side-by-side at two different distances and during social separation

Abstract

When loose-housed dairy goats feed in close proximity to each other, frequent social conflicts are often reported. The aim of this study was to investigate whether the cardiac activity of dairy goats is affected when they are obliged to feed side-by-side in close proximity. In five dyads of goats each stemming from eight groups (8x5 dyads) differing in terms of grouping age and presence of horns, heart rate (HR) and root mean square of successive beat-to-beat differences (RMSSD) as a parameter of heart-rate variability were measured in two experimental situations differing in distance during feeding. Dyads were allowed to feed for 5 min at two hayracks set-up side-by-side at a "far" or a "near" distance. Before goats were exposed to these test situations, baseline values of cardiac activity were measured. The differences of the baseline and test values (Delta) for HR and RMSSD were used for statistical analysis with linear mixed-effects models with crossed random effects. They were tested for dependence on feeding distance, rank within the group, dyadic rank relationship, grouping age, and presence of horns. In addition, cardiac activity was measured in a social-separation experiment conducted with the same goats. Baseline cardiac activity depended on the goat's rank within the group, with higher/lower levels of RMSSD/HR found in high-ranking than in low-ranking goats. In the feeding experiment, a significant interaction (feeding distance*rank within group, p=0.01) was found for Delta RMSSD: Low-ranking goats had lower Delta values at the far than at the near feeding distance. By contrast, high-ranking goats had lower Delta values at the near than at the far distance. In the separation experiment, Delta HR increased significantly compared to the feeding experiment (p<0.05), whereas Delta RMSSD did not differ significantly. Our results show that cardiac response is context-specific in dairy goats (feeding vs. separation), and that the individual's rank within the group must be taken into account in any future studies of their cardiac activity.