Measuring positive emotions in cows: Do visible eye whites tell us anything?

Insight into the emotional lives of animals is of utmost importance to the welfare of the billions of animals in our care, yet little is known about how to measure these states. Scientific understanding of how to measure and interpret positive emotional states is particularly lacking, although recent years have seen a notable increase in such studies. This study explored whether the percentage of visible eye whites is a valid measure of a low arousal, positive emotional state in dairy cows (Bos taurus), by using stroking as the positive stimulus. Thirteen dairy cows were studied over a period of two months, and a total of 372 full 15minute focal observations were performed. Each focal observation comprised three 5minute phases: pre-stroking (baseline), stroking (stimulus), and post-stroking (post-stimulus), and the focal cow's behaviours were recorded throughout each observation, and the focal eye was filmed for later analysis. Following data collection we calculated the percentage of visible eye white at nine pre-determined measurement points throughout each focal observation. The eye white data were analysed using the one-way repeated measures ANOVA test. The percentage of visible eye white dropped during stroking compared with during both the pre-stroking and post-stroking phases (ANOVA: F1.242, 14.9=4.32, P=0.025). The behaviours were analysed using Friedman's ANOVA and Wilcoxon's signed-rank test. Behaviours known to be associated with positive emotions in cows were performed during the stroking phase of the focal observation, supporting the use of stroking as a stimulus to induce a positive, low arousal emotional state. This study has explored the potential of visible eye whites as a measure of positive emotions and arousal, and our results support previous studies which suggest that eye whites may serve as a dynamic measure of emotion and arousal.