CHAPTER 25 Aggression in Horses
Because of their large size, aggression in horses can be very dangerous, whether it is directed to humans, other horses (conspecifics), or other animals. Aggression does not have a single cause. Current internal and external conditions, as well as prior learning, all can contribute to expression of aggressive behavior. Horses exhibit a wide spectrum of aggressive behaviors. Whereas biting, striking with one or both forelimbs, and kicking with one or both hind limbs are all likely to cause bodily harm to whomever or whatever the aggression is directed against, horses also exhibit a variety of behaviors, called threats or intention movements, that do not cause harm but signal the probability that the horse will proceed to harmful aggression if certain changes in their internal or external environment do not occur (Box 25-1). General reasons for the demonstration of aggressive threats or injury-inducing aggression include pain, fear, attempts to control important resources, defense of young, and lack of appropriate socialization or habituation. Use of the word aggression in this chapter refers to both threat behaviors and injury-inducing aggression.
Box 25-1 Intention Movements that Signal the Likelihood of the Horse Carrying Out Injury-Causing Aggression∗
| Threat to bite | The horse moves the head or its whole body closer to the individual being threatened and rapidly opens and closes the mouth. |
| Smack | The horse rapidly opens its mouth, making a loud “smacking” sound as the tongue disengages from contact with the hard palate. This behavior has been observed only in mares with nursing foals and is hypothesized to be a modification of the threat to bite that adapts to the fact that the foal cannot see its mother’s head while nursing. |
| Ears back or head threat | This is a mild form of the threat to bite in which the ears are laid back against the neck while the horse looks at or moves its head or its whole body closer to the individual threatened, without opening the mouth. |
| Threat to strike | The horse raises one or both (partial or full rear) forelimbs and moves them toward the target without making contact. |
| Threat to kick | |
| Squeal | The horse emits loud, high-pitched vocalization. |
| Supplant | This may occur without laying back of the ears. A horse moves directly toward another horse, typically at a brisk walk, resulting in the horse being approached moving away, after which the aggressor occupies the space and uses the resource previously occupied by the supplanted horse. |
| Chase | One horse pursues another at a trot or canter with the ears laid back and sometimes a concurrent threat to bite. |
| Tail lashing | The horse vigorously lashes its tail. |
