Reliable measures of positive emotions in animals are widely needed. We explored whether the percentage of visible eye whites in dairy cows is a valid measure of a low arousal positive emotional state, by using stroking as the positive stimulus. We performed 372 full 15 minute focal observations on 13 habituated cows, filming the focal cow’s eye and recording their behaviours during three phases of the focal observation: pre-stroking, stroking and post-stroking. We then calculated the percentage of visible eye white at nine pre-determined measurement points; three in each phase of the focal observation.

We analysed the visible eye white data using the One-Way Repeated Measures ANOVA test. We found that the percentage of visible eye white dropped significantly during stroking, compared with during both the pre-stroking and post-stroking phases (F_{(1.242, 14.9)} = 4.32, p = 0.025). We controlled for high arousal behaviours, and we analysed the performance of behaviours known to be associated with positive emotions in cattle. ‘Stretching neck’ for example, was performed significantly more during stroking than during pre-stroking or post-stroking (X²₂ = 700.68, p = 0.000). This and the performance of affiliative behaviours such as ‘leaning into stroker’ provide support for the use of stroking as a stimulus to induce a positive emotional state in this study.

This study has built upon existing work in this field to provide greater insight into the use of visible eye whites as a measure of emotional state in cattle. Our study specifically focused on the effect of a change in valence, rather than on a change in arousal as done previously. Our results therefore provide helpful insight into the relationship between visible eye whites, valence and arousal and support previous studies which suggest that visible eye whites may serve as a dynamic measure of emotional state in cows.