Development of a consensus definition of “separation anxiety” for horses

Horses are separated from other horses as part of routine management practices, such as for training, transport, competition or veterinary procedures. However, being separated from a close companion or being isolated from all other horses are both potentially stressful scenarios for a socially gregarious species like the horse, and some individuals can struggle to cope with this. In addition to social isolation, for a species with strong intraspecific group bonds, separation from an individual to whom the horse is particularly bonded, even with others still present, may also result in distress. What is commonly referred to as separation anxiety is not simply about being alone but may also relate to the loss of anyone to with whom the horse has a close bond. Therefore, the aim of this study was to better understand the nature of what is described as separation anxiety in horses and to build a consensus for the definition of this complaint for future research purposes, considering the contexts in which it may happen and the potential behaviours which can be expressed. To achieve this goal, we sought owner and caregiver opinion on separation anxiety in horses. Content analysis of the transcribed responses was conducted to reveal distinct definitions and contexts of separation anxiety along with the common signs shown by horses with separation anxiety. This was followed by an equine behavioural expert consensus exercise to provide external face validity for our analysis. We highlighted eight different contexts defined along two axes: one based on whether the horse is left behind or actively leaving the group, the other on the timing of the response within the separation process; this was separated into: during ‘preparation’ for departure; when ‘actively leaving or being left behind’; when there is an ‘initial barrier to contact’ and finally when there is a ‘loss of contact’. Moreover, we identified several signs potentially associated with separation anxiety, ranging from increased arousal (e.g., increase locomotor activity, hypervigilance) to ‘apathy’. We provide a theoretical model that integrates this information to illustrate the phenomenon commonly referred to as “separation anxiety in horses”. Future work can test the predictions made here and their clinical implications. • Being separated or isolated from another is a potentially stressful scenario • There is no clear definition of separation anxiety (SA) in horses • Eight contexts potentially giving rise to SA were identified for horses • Specific signs may help to different define meaningful forms of SA • A theoretical model of SA in horses is proposed