Why do horses yawn? It’s still a mystery, or perhaps there are multiple mysteries to be investigated. We all observe horses yawning, but does it seem like some yawn more than others? And are there times when a horse yawns more often?

Science is whittling away at the yawning mysteries and this week we have some new research to contemplate, as a study has been published compared the yawning behavior of wild (Przewalski) horses compared to domestic horses living in similar conditions.

A horse’s yawn, by the way, was defined by Sue McConnell, PhD in 2003 as “Deep long inhalation with mouth widely open and jaws either directly opposed or moved from side to side”. Yawning is related to some gastrointestinal conditions, and has been proposed as communicating between horses, and reaction to stress. Could a high level of yawning mean that a horse’s welfare is compromised?

The newest research, published this week under an Open Access license (so you can read and download it without charge), builds on previously published equine behavior research, such as a study by Fureix and colleagues in France. Fureix studied horses living in stalls and recorded stereotypic behavior, such as cribbing and weaving, and the frequency of yawning.

While not all horses yawned, horses that did yawn repeatedly exhibited stereotypic behaviors. This raises the question of the role that stress plays in yawning, as well as the role that living in stalls might play in increasing stress in horses. Might confinement and social isolation trigger both the yawning and the stereotypies in domesticated horses? Was confinement the x factor?

If confinement is x, the y factor might be social isolation. Would stress levels decrease in horses living in pasture groups? Do horses living in turnout yawn as much? What about horses in the wild, particularly Przewalskis, which are a separate subspecies from our domestic Equus Caballus friends?

Lead author Aleksandra Górecka-Bruzda moved the research ahead by studying horses in natural settings rather than horses that live in stalls.

Two groups of horses were observed to see how often they yawned. One group was Przewalski horses in a preserve, the other was a group of saddle horses living together in a semi-natural turnout situation that was considered close to ideal. Would they find that, by comparison, stall-dwelling domestic horses yawned more than outdoor-dwelling horses? Would the social factor of turnout life increase or decrease yawning behavior?

If stress from confinement is x, the y factor might be social isolation. Would stress levels decrease in horses living in pasture groups? Do horses living in turnout yawn as much? What about horses in the wild, particularly Przewalskis, which are a separate species from our domestic Equus Caballus friends?

Lead author Aleksandra Górecka-Bruzda, PhD, DSc, of the Institute of Genetics and Animal Breeding In Warsaw, Poland moved the research ahead by studying both subspecies of horses in natural settings rather than horses that live in stalls. The research team included Carole Fureix, PhD, MSc, BSc, of the University of Bristol in the United Kingdom, the author of the earlier study on yawning behavior in horses living in stalls.

Two groups of horses were observed to see how often they yawned. One group was Przewalski horses in a preserve, the other was a group of saddle horses living together in a semi-natural turnout situation that was considered close to ideal. Would they find that, by comparison, stall-dwelling domestic horses yawned more than outdoor-dwelling horses? Would the social factor of turnout life increase or decrease yawning behavior?

The authors found that other factors, such as testosterone levels in male horses, and the heightened stress of social interaction, increased yawns in some horses, particularly stallions. But the domestic horses did not yawn more often than the Przewalskis when kept in a natural living situation. The Przewalskis yawned when exhibiting aggressive social behavior, but they also engaged in more social situations than the domestic horses did.

Ultimately, the researchers found that yawning in the domestic horses had social context, and that yawning might be a displacement activity to release tension.

Their conclusion found good reason to consider frequent yawning in a welfare evaluation of a horse: “Since a high frequency of yawning was related to increased frustration in horses kept in a restricted stabling environment, it may also be supposed that the lower frequency of yawning in horses observed in undisturbed social groups may reflect increased welfare in equine groups living in favorable conditions satisfying their behavioral needs. Increased occurrence of yawning in domestic situations could thus attract the attention of caretakers to make the alterations to improve the welfare of their horses.”

If that is the case, can stables be blamed once again for causing yawn-response stress in horses? Studies from several countries have recently advocated for more natural living situations for horses, or at least for stable designs that increase sight lines and possibilities for social behavior. Obviously, the amount of time a horse spends in a stall affects how stressful stabling is. And, for some horses, turnout is a stressful experience.

Research is conducted to increase the body of knowledge; other researchers use it to carry on studying horses and build the knowledge further. In some research, the goal is to provide information of direct benefit to horses via informing owners and caretakers of findings. Other research is for the benefit of comparing horses to other species, or even to humans.

Horse owners should be aware of new research, but also be aware that many studies use small numbers of horses in tests, and that horses live in many different types of environments and have different medical histories, ages, breeds and sizes. In order stand the test of time, research must be repeatable and yield the same or similar results when tested by others.

While the authors in this study don’t state it in as many words, they do not say that an absence of yawning is a sign that horse has no stress, nor do they say that yawning alone is an indication for welfare concern.

Horses that exhibit stress may respond to many changes in their care, such as who is in the next stall, whether there is a window, or how often or when they’re fed. Likewise, turned out horses react to the horses in their groups, how close it is to feeding time, or the fact that they’re bothered by flies or mud or a blanket that doesn’t fit.

Wise horse owners spend a good deal of time just watching their horses, and learning what is normal. How often does a horse usually roll? Is a horse normally seen trotting along the fence line? Which horse comes to the gate first to be brought in and which one comes in last?

And now we can add: which ones yawn, and where do they do it?

Thanks to The Science of Nature, a monthly peer-reviewed scientific journal published by Springer Science+Business Media, for the Open Access publication of this and other papers on equine health and behavior. The article will be published in the October 2016 edition of the journal and may be viewed and downloaded online now.

Citation

Investigating determinants of yawning in the domestic (Equus caballus) and Przewalski (Equus ferus przewalskii) horses

Aleksandra Górecka-Bruzda, Carole Fureix, Anne Ouvrard, Marie Bourjade, Martine Hausberger Science of Nature (2016) 103: 72. doi:10.1007/s00114-016-1395-7

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