The physiological consequences of crib-biting in horses in response to an ACTH challenge test.

This research investigates the phenomenon of “crib-biting”, a repetitive behavior seen in horses, and whether preventing this behavior could have negative outcomes on the horse’s stress levels. The authors found that horses who exhibited crib-biting behaviors had higher cortisol levels, an indicator of stress, than horses that did not display this behavior, suggesting that crib-biting may function as a coping mechanism during stress and that preventing the behavior may not be beneficial.

Study Overview

• The driving question of the research was whether stereotypic behaviors like crib-biting were functional coping mechanisms that help to regulate stress in animals.
• The conducted their investigation by observing and monitoring two groups of horses: a group of 22 horses affected by crib-biting (Group CB) and a group of 21 horses who did not display this behavior (Group C).
• You can think of crib-biting as the horse equivalent of nervous twitches or fidgeting many humans exhibit when stressed.

Methodology

• The researchers triggered physiological responses in both groups using an Adrenocorticotropic hormone (ACTH) challenge test – basically a stress test for horses. The test involved the administration of an ACTH injection, which stimulates cortisol production and thus, stress response.
• Following the injection, the researchers measured both saliva cortisol (an indicator for stress) every 30 minutes, and checked heart rate (HR) continuously for three hours.

Results

• No difference was found in heart rate or heart rate variability between the crib-biters and controls. However, the horses displaying crib-biting behavior had significantly higher cortisol responses than those in the control group, suggesting a higher stress level in the former.
• This result was consistent with an exception: among the horses presented with the ACTH stress test, those who didn’t perform crib-biting during test (Group B) had even higher levels of cortisol levels than the rest of their group. This indicates that the horses perform crib-biting as a means of relief from the induced stress. Horses who were allowed to crib-bite during the test (Group A) had lower cortisol levels in their saliva.

Conclusion

• The findings from this study offer strong evidence supporting the hypothesis that crib-biting is in fact a coping mechanism by which horses manage stressful situations, helping them to reduce cortisol levels.
• It suggests that preventing horses from exhibiting such stereotypic behavior, though it might appear abnormal or disruptive, may in fact be counterproductive as it stops them from managing situations they deem stressful. Possible implications of this could mean a re-evaluation of measures taken to stop such behaviors.