Why does my horse keep yawning?

 the alertness of the others, as they may need to become more vigilant in watching for predators to compensate for the tired group member. Interestingly one study proved that yawning can be contagious between humans and dogs. Pet dogs respond more frequently to the yawns or their owners than those of strangers. No such link has been shown in horses as yet. Perhaps it is worthy of some investigation next time you are at the stables!

But what about horses?

In horses, yawning has been defined as a “deep long inhalation with mouth widely open and jaws either directly opposed or moved from side to side”. It seems to occur far less frequently in horses in comparison to humans or carnivores. In the vast majority of cases, the occasional yawn will indicate a state of relaxation. However, there may be other reasons behind yawning, particularly if it becomes a more frequently observed action. 

Like humans, horses have been shown to demonstrate more frequent yawning behaviour in response to increasing ambient temperatures. One study observed horses that were given free access to a choice of three paddocks, one in full sun, one in shade and one cooled by water. The horses yawned more often while in the sunny field, strengthening the hypothesis that it is linked to a need to cool the brain. 

Dominance or aggression

Primates use yawning-like behaviour as a threat to assert dominance or demonstrate aggression, as well as in response to a change in arousal state or stress. In horses, a small research study comparing wild Przewalski horses and their domestic counterparts demonstrated a positive correlation between aggressive behaviours and yawning frequency. This behaviour was more pronounced in entire males in both the wild and domestic groups suggesting a link between testosterone induced aggression and yawning.