Ricci-Bonot, C., Mills, D. S. 2023. Recognising the facial expression of frustration in the horse during feeding period. Applied Animal Behaviour Science 265, 105966.

Horses often present negative emotional states which are frequently poorly recognised, with much of our understanding of horse expressions based on anecdotes, rather than scientific evidence. The aim of this project was to identify potential facial markers of emotional states. 31 horses, aged between 2 and 23 years old (mean ± SD: 11.5 years, ± 6.6) and various genders (1 male, 10 geldings and 20 females) took part in the study. They were tested in three different scenarios involving the potential availability of food. Horses were trained to anticipate a reward after 10 s and then tested across the following three situations. Anticipation of a reward, considered a positive emotional state; frustration at waiting for a reward and disappointment at the loss of the reward - both considered negative emotional states. Tests were conducted in a stable with a feeding device fixed outside the stable within reach of the horse. Analysis of video recordings of facial expressions of the horses was undertaken using the Horse Facial Action Coding System (EquiFACS), an objective system for coding facial movements on the basis of the contraction of underlying muscles, as well as their behaviours. Specific facial markers associated with anticipation could not be characterised, however, we found that the occurrence of 9 actions and behaviours differed significantly between the two situations predicted to induce frustration and disappointment during the feeding period. The frustration phase was characterised by a higher likelihood of ‘eye white increase’ (AD1), ‘ear rotator’ (EAD104), and ‘biting feeder’ compared to the ‘disappointment’ situations. By contrast, ‘blink’ (AU145), ‘nostril lift’ (AUH13), ‘tongue show’ (AD19), ‘chewing’ (AD81) and ‘licking feeder’ were more likely in the ‘disappointment’ phase than in the ‘frustration’ situation. There was also a general gender effect with females more likely to blink than males. The findings of this research may help differentiate frustration and disappointment at least during the feeding period.