Crib-biting Behaviour of Horses: Stress and Learning

Fri, 03/31/2017 - 13:01
Veterinary News

Crib-biting is a stereotypy in horses that is potentially linked to both chronic stress and genetic predisposition. Chronic stress can cause neurobiological changes such as alteration of the dopaminergic modulation of the basal ganglia, which could alter the learning profile of the horses.

Briefer, Beuret, Briefer, Zuberbühler, Bshary and Bachmann, who work for the Swiss National Stud and at the Institute of Biology, of University of Neuchâtel, and at the Institute of Agricultural Sciences at the ETH Zurich, conducted a research into cribbing. They presented their findings at the 2016 International Equitation Science Conference in Saumur, France, on 23 - 25 June 2016

The Study

The Swiss researchers tested 19 crib-biters and 18 non-crib-biting horses (controls) in five challenging spatial tests, in order to test if potential differences in dopaminergic modulation impair learning capacities. The tests were performed in two parts, separated by a break, in a small arena (8 x 10m) that was familiar to the horses. For each trial (phase 1: 21 trials; phase 2: 12 trials), the horses were led to the start zone in front of a solid fence (4m) and were then left alone in the arena. Their task was then to find a bucket containing food, which was situated at different locations around the fence, depending on the tests. The time to reach the food bucket (Time) and the trajectory taken by the horse (left or right side of the fence) were recorded continuously. Additionally, salivary cortisol was collected before the tests (baseline), after phase 1 and after phase 2.

Crib-biters and controls behaved similarly during the learning tests. However, crib- biters that did crib-bite on the solid fence during the task (group A; 10 horses) behaved differently than crib-biters that did not crib-bite (group B; 9 horses) and controls (group C; 18 horses) for some of the tests (e.g. Time, Linear mixed model).

These differences are likely explained by the time taken to crib-bite, more than by differences in impairment of the dopaminergic system. Indeed, the frequency of crib-biting affected Time for the tests where a group difference was found. We also found a difference in salivary cortisol after the phase 1, between groups A, B and C; the crib-biters that did not crib- bite had higher salivary cortisol values than all the other horses.

The results suggest that crib-biting horses that did not crib-bite during the learning tests were more stressed than all other horses. This difference could be due to higher stress sensitivity in crib-biters, which could be reduced by the opportunity to crib-bite. Therefore, we suggest that letting the crib-biters crib-bite will improve their welfare

Conclusion

Crib-biters and control horses generally behaved similarly during the learning tests, with the exception of some of the crib-biters that did crib-bite during the learning tests. Additionally, crib-biters that did not crib-bite during the learning tests were more stressed than all other horses. We suggest that the opportunity to crib-bite helped the crib-biters to reduce their stress and improved their welfare.

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