Physiological and behavioral consequences associated with short-term prevention of crib-biting in horses

Crib-biting in the horse is frequently prevented in the short-term by horse-owners using physical means. Because it has been proposed that crib-biting may function to reduce stress, the effect of prevention of crib-biting and/or eating on the behaviour, heart rate, and plasma cortisol and beta-endorphin concentrations was measured in six crib-biting and six normal horses. When crib-biters were unable to crib-bite, they showed an increase in ingestive behaviour. When crib-biters were prevented from crib-biting and eating, a relative stasis in the motility of the foregut occurred, suggesting that normal gut function in these animals depends on ad libitum access to food and to suitable crib-biting substrates. There was no significant difference in the mean baseline levels of normal and crib-biting horses but, contrary to expectations, beta-endorphin levels were higher in crib-biting horses than in normal horses when crib-biting was prevented. Mean baseline levels of cortisol were higher, under a variety of test and control conditions, in crib-biting than in normal horses, but there was no significant rise in cortisol levels in crib-biters during periods when crib-biting was prevented, suggesting that the function of this oral stereotypy does not lie in stress-reduction.