The Effect of Diet on Equine Stereotypic Behaviours

Cribbing is a compulsive behaviour or stereotypy that is bothersome to many horse owners because of the damage it may cause to both the horse and the farm itself. While cribbing, the horse places his upper incisors on the surface of the object, flexes his neck, pulling against the object, and sucking in air. 

There are many beliefs as to why horses begin and continue to crib. Most believe that horses crib in response to boredom or frustration. Others feel these stereotypies are learned behaviours. While there is evidence of a heritable component to cribbing, studies have shown that very few cases are a result of watching other horses perform these behaviours. A decrease in gastric pH has also been shown to increase the frequency of cribbing in horses. 

Yet increasing evidence suggests that dietary factors influence the development of abnormal behaviours, including cribbing, wind sucking, and wood chewing in horses. Positive associations have been detected between stereotypy prevalence and low forage/high starch rations. It has been suggested that these stereotypies develop very early in life. Studies have shown that horses receiving large amounts of grain after weaning had a significantly greater risk of developing cribbing than those that did not. The rate of development of stereotypic and redirected behaviour was shown to be greatest during the first nine months of life.

The aim of a recent study was to compare in detail the behaviour of young horses fed two different diets, one a conventional starch and sugar based diet at 37 percent nonstructural carbohydrates (NSC), the other based on fat and fibre at 25 percent NSC. Seventeen part-bred Thoroughbred horses were used in the trial. Horses were kept outside in grass pastures with their mothers 24 hours a day from birth to approximately six months of age. During this period they were fed twice a day in close proximity to their mothers, although mares were not allowed to access the feed.

Clear differences were apparent in the hours after weaning. Overall, the effects of the fat and fibre diet on behaviour expressed during the temperament tests and at weaning showed unexpected consistency. The fat and fibre horses appeared less distressed immediately after weaning, and were less flighty, more willing to perform, and possibly more attentive or sensitive to their environment than the sugar and starch horses. While the current study did not detect cribbing in the horses, it was evident that dietary source of energy had a significant effect on the behaviour of younger horses specifically during periods of stress. It is feasible to suggest that other times of high stress such as breaking would also elicit similar responses and may benefit from a higher forage and fat type diet.