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Horses occasionally display abnormal oral behaviors such as excessive licking, sham chewing, and bedding consumption. These behaviors could reflect poor welfare, such as unpleasant living conditions or chronic stress. One study shows that altering the diets of horses with abnormal oral behaviors by providing more forage and fiber decreases the frequency of these behaviors and improves health.*

Abnormal oral behaviors were observed in horses housed at a single facility. Twelve of those horses were used in a study designed to examine the effect of diet modification on abnormal oral behaviors. All horses exhibited behaviors described as either oral stereotypic behaviors or redirected behaviors. Oral stereotypic behaviors included sham chewing (i.e., making chewing movements when no food is present in the mouth) or repetitive licking of inanimate objects. Researchers defined redirected behaviors as the result of insufficient appropriate stimuli, so the behavior is redirected to alternative stimuli. Boredom or nutritional imbalance may lead a horse to coprophagy or wood chewing, both examples of redirected behaviors in horses fed low-fiber diets.

Horses were divided into two groups: a control group in which horses showed a low frequency of these behaviors and a treatment group that showed multiple abnormal oral behaviors with a greater frequency than horses in the control group. Horses in the control group were maintained on a standard high-concentrate, low-fiber diet, whereas horses in the treatment group consumed a high-forage, high-fiber ration.

“The high-concentrate diet consisted of alfalfa (lucerne) hay, wheat chaff, and a concentrate. The high-forage diet was formulated by adding timothy hay to the ration and reducing the amount of concentrate,” explained Ashley Fowler, Ph.D., a nutritionist for Kentucky Equine Research.

The effect of the diet change on behavior was assessed by measuring the amount of time horses spent displaying abnormal oral behaviors, both oral stereotypies and redirected behaviors. In addition, cortisol, also known as the “stress hormone,” ghrelin, and leptin were measured. Ghrelin regulates food intake and plays a role in stimulating hunger, and leptin is produced by white adipose tissue to create the sensation of satiety.

Researchers compared changes between treatment and control groups at the start and end of the 30-day trial.

“The time spent on abnormal oral behaviors significantly decreased in the treatment group over the 30-day study period. Specifically, oral stereotypies decreased by 70% and redirected behaviors decreased by 86%,” Fowler explained.

In addition, abnormal oral behaviors were significantly lower for horses fed the high-forage diet compared to the control group at the end of the study period. Manure eating was not observed in the treatment group during the study period, and less time was spent on oral stereotypic behaviors and bedding consumption in the high-forage group.

This study also found that the mean plasma cortisol and ghrelin levels decreased by 30% and 20%, respectively, in the treatment group over the 30-day trial. These hormones were also significantly lower than the control group by the end of the study.

“For leptin, values increased by 16% in the treatment group over the 30-day study and were 18% higher in the high-forage group than the high-concentrate group at the end of the study,” Fowler said.

According to the research team, ghrelin and leptin changes support the hypothesis that oral stereotypic behaviors and redirected behaviors appear to derive from failure in feeding motivation and lack of satiety.

“In other words, the high-forage ration provided longer satiety compared to the high-concentrate diet,” explained Fowler.

She added, “This study shows that diet can influence behavior and hormone levels in horses. Ensuring horses have sufficient fiber in their diet can therefore affect the overall health and well-being of horses.”

According to Fowler, timothy hay was added to the diets of horses included in the study to increase fiber content. For horses requiring more energy in their diets than provided by hay alone, consider adding fibrous stuffs such as soy hulls and beet pulp.

“When feeding a forage-based diet, it is important to balance the vitamin and mineral content of the ration, as most forages are low in some trace minerals. Adding a well-formulated vitamin and mineral supplement will help ensure the horse’s nutritional requirements are being met,” Fowler recommended.

*Hanis, F., E.L.T. Chung, M.H. Kamalludin, and Z. Idrus. 2023. Effect of feed modification on the behavior, blood profile, and telomere in horses exhibiting abnormal oral behaviors. Journal of Veterinary Behavior 60:28-36.


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