Ethogram for understanding horse emotions and social behaviour

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 Researchers at the University of Portsmouth’s Centre for Comparative and Evolutionary Psychology have developed the first anatomically-based ethogram of equine facial behaviour, offering a tool for understanding how horses communicate through facial movements. This ethogram—essentially a structured catalogue of facial actions—captures how domestic horses use their faces to convey emotions such as curiosity, aggression, playfulness, and attentiveness across a variety of social contexts.

Unlike the term “facial expression,” which often implies an associated emotion, the researchers have deliberately used the term facial behaviour. This distinction acknowledges that while some facial movements may correlate with emotional states, not all facial changes are necessarily expressive in the emotional sense. This neutral terminology allows for more objective observation and coding of equine facial movements.

 

The aim of the study was to develop an ethogram of equine facial behaviour observed during horse-horse interactions. These interactions were categorised into affiliative (non-play), play, agonistic (conflict), and attentional contexts. Using the Equine Facial Action Coding System (EquiFACS)—an established method that links visible facial changes to specific underlying muscle movements—the researchers documented 805 facial expressions across 22 distinct behaviours.

 

Crucially, they employed a novel statistical tool to analyse how these facial actions cluster in different social scenarios, providing new insights into the functional roles of facial behaviour in equine communication.

 

The study revealed that horses exhibit a wide and nuanced range of facial behaviours depending on the social context:

 

Agonistic Interactions
Aggressive or conflict-based interactions were marked by flattened, backward-facing ears, inner brow raisings, nostril dilation, and head-lowering. These signals offer clear warnings of potential escalation, helping horses (and human observers) anticipate and de-escalate conflict.

 

Attentional States
When alert or investigating their environment, horses displayed forward-pointing, closely positioned ears. Additional markers included increased blinking or half-blinking, and head positions that facilitated sensory focus, such as lifting the head to enhance visual attention.

 

Friendly Interactions
Interestingly, affiliative interactions were often characterised by relatively neutral facial behaviour. Contrary to the common belief that ears forward indicate positive emotion, this was not consistently observed. This suggests that minimal facial movement in these contexts may actually signal comfort and positive mood—highlighting the importance of considering the broader behavioural and social context.

 

Play Behaviour
Playful interactions involved the most dynamic facial displays, including dropped lower lips, raised chins, parted lips, open mouths, flattened or rotated ears, prominent eye whites, and forward-thrust nostrils. Many of these expressions resemble the open-mouth play faces seen in primates and carnivores, supporting the idea of a shared evolutionary origin for certain play behaviours across mammalian species.

 

“We found that horses often use the same facial movements across different contexts, but the combinations and intensities vary,” explained Dr Kate Lewis, lead author. “This flexibility underscores the importance of considering the whole body and context when interpreting equine behaviour.”

 

One of the most intriguing findings was the identification of a previously unrecorded facial movement, designated as AUH21, involving the platysma muscle. (The platysma muscle  is a thin, superficial muscle located just beneath the skin. It extends along the side of the face and neck, originating from the region near the ear and inserting into the skin of the neck and shoulder. Its primary function is to move the skin, aiding in facial expressions and helping to twitch the skin to repel insects.)This movement causes tightening on the side of the face, making the underlying anatomical structures more visible. AUH21 has previously only been documented in humans and gibbons, making its discovery in horses significant for comparative biology. It may also offer new avenues for evaluating emotional states and pain indicators in equine clinical settings.

 

By providing a scientifically validated reference for interpreting equine facial behaviour, the ethogram is poised to become a vital resource for equine veterinarians, behaviourists, trainers, and students of equine science.

 

“This is the first time we’ve been able to systematically document how horses combine facial movements into meaningful expressions,” said Dr Leanne Proops, Associate Professor in Animal Behaviour and Welfare. “It opens up new possibilities for understanding equine emotions and improving welfare.”

 

The study is published in PeerJ, along with the full ethogram and supporting analyses, offering a robust framework for further research and practical application.

 

“This work is a game-changer for anyone working with horses,” Dr Proops added. “It gives us a new lens through which to view and interpret their behaviour, ultimately leading to better care and stronger human-animal relationships.”

 

For more details, see: 

 

Lewis K, McBride SD, Micheletta J, Parker MO, Rincon AV, Wathan J, Proops L.(2025). 

An ethogram of facial behaviour in domestic horses: evolutionary perspectives on form and function. 

PeerJ 13:e19309

https://doi.org/10.7717/peerj.19309