Crib-biting seems to provide some beneficial feedback to horses who indulge in the behaviour, according to Swiss researchers.
Sabrina Briefer and her colleagues from several Swiss academic institutions set about trying to find physiological differences between crib-biters and control horses.
The researchers, reporting on their findings at the recent International Equitation Science Conference in Denmark, said crib-biting was among a number of stereotypies – repetitive patterns of behaviour which are apparently functionless – observed in a wide range of species in captivity.
They can occur, they said, when a situation exceeded the natural regulatory capacity of the animal, and particularly in situations that included unpredictability and uncontrollability, giving rise to chronic stress.
“Many studies have proposed that stereotypic behaviour may serve as a coping mechanism, but results are contradictory,” they said.
They measured the endocrine responsiveness of 21 crib-biters and 21 control horses after inducing a stress response in the horses by using what is known as a adrenocorticotropic hormone (ACTH) challenge test. The hormone is used to trigger a stress reaction through stimulating the adrenal glands.
Heart rate was measured continuously and salivary cortisol levels – another stress indicator – were taken every 30 minutes for three hours.
The researchers found no difference in heart rate between groups.
However, the crib-biters had a higher cortisol response during the ACTH challenge test.
“Interestingly, it seems that this difference in cortisol was largely due to the crib-biters that did not crib-bite during the test,” they reported.
“Indeed, these horses had higher cortisol responses than all other horses.”
The researchers said their results suggested that crib-biting horses differed from control horses in the reactivity of their hypothalamic-pituitary-adrenal axis.
“This difference could be a consequence of chronic stress and/or genetic predisposition,” they suggested.
“Crib-biting might be a successful coping strategy that helps horses to gain control over situations and reduces cortisol levels.”
They concluded that crib-biters might have a gene-related difference in their hypothalamic-pituitary-adrenal axis and that the behaviour seemed to have some beneficial feedback.
“Preventing crib-biters to crib-bite could be counter-productive because this behaviour seems to have some beneficial feedback for horses,” they told delegates.