The common practice of preventing equine stereotypic behaviour in the UK may be of concern, from a welfare perspective, if these behaviours constitute a coping response to a suboptimal environment. The aim of this study was to assess the putative function of these behaviours by measuring behavioural and physiological parameters i) before and after stereotypy prevention; ii) before and after stereotypy performance; and iii) in response to opiate antagonist (naloxone) administration.
The crib-strap significantly (P = 0.05) elevated mean plasma cortisol levels in crib-biting horses; a similar, although not significant trend (P = 0.07) was also observed for the weaving group during the anti-weave bar treatment. Both crib-strap and anti-weave bar significantly (P < 0.05) elevated plasma cortisol levels in the control horses. Although the latter result prevented a definite conclusion being drawn about the function of equine stereotypies, the results did indicate that the use of the crib-strap and anti-weave bar is stressful to the horse.
Plasma cortisol level was significantly (P = 0.04) higher immediately prior to the onset of stereotypy followed by a significant reduction post-stereotypy. This suggested that both crib-biting and weaving have a coping function to reduce stress levels in the animal.
Naloxone significantly reduced crib-biting by 84 per cent (P = 0.05) but it did not reduce weaving behaviour, indicating that crib-biting is a reward behaviour. However, resting behaviour was also significantly (P = 0.02) increased in crib-biting horses, suggesting that the stereotypy reduction was due to a sedative effect of the opiate antagonist. The latter was not measured, however, in control or weaving animals, and thus may be interpreted differently. The welfare implications of these results are discussed.