Heart rate and behavioural responses of crib-biting horses to two acute stressors.

The research looked into the heart rate and behavioral differences between crib-biting and non-crib biting horses when subjected to two stress factors. It was found that crib-biting horses had higher average heart rates, responded less strongly to being restrained with a lip twitch, and reacted more strongly to the sudden inflation of a balloon.

Subjects of the Study

• The study involved 14 adult saddle horses, divided into two groups based on their behaviour: eight crib-biters and six normal controls.
• Crib-biting is a compulsive behaviour in horses wherein they bite onto a solid object such as the railing of their stall, arch their neck, gulp in air and let out an audible grunt.

Procedure and Measurements

• Initially, the scientists studied the relationship between crib-biting and heart rate in undisturbed conditions.
• The researchers then exposed the horses to two different acute stressors: restraining them using a lip twitch, and exposing them suddenly to the rapid inflation of a balloon.
• The researchers took note of the heart rates of the horses during these situations, as well as their behaviour post exposure to the stressors.

Key Findings

• The heart rate of the crib-biters was lower during periods of crib-biting compared to other activities. However, crib-biters generally had a higher overall mean heart rate, pointing to the likelihood of higher basal sympathetic activity (part of the nervous system response related to stress and the ‘fight or flight’ response).
• All horses exhibited a temporary increase in heart rate after being restrained with a twitch. However, the heart rate in crib-biters reverted to base rates faster.
• Crib-biters were less reactive to the lip twitch application with only one out of six showing significant discomfort. Following the release of the twitch, they also spent more time nibbling compared to the control group.
• The crib-biting group exhibited a stronger reaction to the sudden inflation of a balloon with half of them reacting noticeably. Following the balloon’s inflation, these horses also spent more time walking in their boxes.