Brain Dysfunction in Cribbing Horses Gives Researchers Something to Chew On

In the first study of its kind, researchers from the United Kingdom have discovered that cribbing horses learn differently than horses that don't crib.

Cribbing is a stereotypy in which a horse grasps an object between his incisor teeth and inhales air into the esophagus while emitting an audible grunting noise. It is the most common stereotypy among stabled horses.

Previous research has suggested that changes in the chemical pathways in specific regions of the brain appear to be important in environmentally-induced stereotypies such as cribbing. In particular, cribbers reportedly have fewer types of dopamine receptors in a specific region of the brain referred to as the dorsomedial striatum.

"Post-mortem studies have illustrated that crib-biting horses have differences in some brain areas," explained Matthew Parker, MSc, a doctoral candidate in the School of Psychology at the University of Southampton. "We wanted to see how this affected their learning."

The purpose of this study was to determine if cribbers respond differently than horses that don't crib in the different phases of learning. The scientists evaluated the horses by examining the relative value of rewards according to different delays--specifically, whether they could learn how to choose a "rich" reward over a "lean" alternative.

illustration showing the brain of a cribbing horse

Cribbers reportedly have fewer types of dopamine receptors in a specific region of the brain referred to as the dorsomedial striatum (shown as red area).

In each session, four normal horses and four cribbing horses were exposed to a red or green light, each associated with a specific plate the horse was to touch with its muzzle. During this phase, they could obtain a treat by pressing the muzzle plate for 10 seconds (red) or 20 seconds (green). The optimal strategy was to press the red side more often during the course of the procedure.

"The results of our study found that noncribbing horses made more responses than crib-biters to the red side, and that the number of correct responses increased over three sessions, showing the normal horses learnt the discrimination easily," explained Parker. "In the crib-biting horses, no improvement was observed.

The authors said these findings support the notion that cribbing might develop as a result of an environment unsuitable for the species, combined with genetic predisposition.

The authors suggest that to avoid cribbing in their animals, owners should ensure horses are kept in suitable environments , with adequate access to forage, social contact, and turnout.

The study, "Impaired instrumental choice in crib-biting horses (Equus caballus)," authored by Parker; Redhead, PhD; Goodwin, PhD, and; McBride, PhD, appears in the current edition of Behavioural Brain Research (Volume 191, pages 137-140).

About the Author

Stacey Oke, DVM, MSc

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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