Self-mutilation behaviour in stallions

Self-mutilation behaviour in horses includes various combinations of self-biting, stomping, kicking and rubbing against or lungeing into objects. An early survey report has estimated that selfmutilation has been observed in as many as 2% of domestic stallions [1]. While at one time prevailing thought held that selfmutilation was principally a stallion behaviour problem [2], it can occur in geldings and mares, as well as in prepubertal animals. Although the form, frequency and intensity of self-mutilation can vary considerably among individuals, it can reach levels that are fertility and/or life-threatening.
Based on their root cause, 3 distinct types of self-mutilation have been recognised in horses [3]. Careful evaluation of the horse’s behaviour is often necessary to distinguish the specific type and to most effectively recommend further diagnostics and interventions.
One type (type I) represents normal behavioural response to continuous or intermittent physical discomfort. In the author’s experience the type comprises the majority of self-mutilation in horses, whether stallions, geldings or mares of any age. By careful study of the horse’s behaviour before, during and after events, this type can often be readily differentiated from the other types. Self-directed biting due to physical discomfort at the time is characterised by (a) variable form and sequence, (b) sudden interruption of ongoing goal-directed behaviour such as eating or resting, often along with (c) less demonstrative indications of discomfort associated with or at times other than self-mutilation events. Self-mutilation resulting from physical discomfort can be provoked or exacerbated by social or handling situations that can be misleading as to the type. For example, for some stallions, self-mutilative events may occur in association with thwarted sociosexual situations, such as another stallion or a mare passing within sight or sound, or as delivery of a food meal is delayed. These associations can easily be misinterpreted as indication that the social situation is the root cause, rather than an exacerbating factor. Also, horses quickly learned predictors of increased discomfort, for example, work. […]