Positive and negative emotions in dairy cows: Can ear postures be used as a measure?

Applying objective measures to assess the emotional states of animals is an important area of research and essential for improving animal welfare. In this study, we have built upon previous research to test whether ear postures can be used as an indicator of emotional states in dairy cows. By using a positive and negative contrast paradigm, we elicited the emotional states of excitement and frustration in 22 dairy cows. Each cow was first conditioned to expect the delivery of standard feed when a bell was rung. Once they were familiar with the experimental set-up and the delivery of the feed, they were then given concentrates feed instead. As concentrates are highly desired, this was considered to elicit the emotional state of excitement. This was then repeated five times. On the following trial, the cows were given inedible woodchip, and the cows' unfulfilled expectations were considered to elicit a state of frustration. We observed the cows' ear postures and mean heart rate (beats per minute) during 15-minute focal observations, each comprised of 5 minutes of pre-feeding (baseline), 5 minutes of feeding, and 5 minutes of post-feeding. Both the woodchip treatment and the concentrates elicited significantly higher mean heart rates compared with the standard feed, indicating that both treatments elicited a high arousal emotional state. The woodchip and concentrates treatments were also significantly associated with the increased performance of different ear postures, indicating that cows do perform certain ear postures in relation to both positive and negative high arousal emotional states. Our results complement previous research performed with both cows and sheep, and indicate that with training and contextual knowledge, ear postures may be suitable as a reliable measure of emotional state in dairy cows.