Burk concluded that wearing grazing muzzles for 10 or 24 hours does not induce stress or affect voluntary exercise. It does, however, alter behavior. | Photo: Courtesy Kristena Davis

Amy Burk, PhD, associate professor at the University of Maryland, in College Park, along with her graduate student, Kristina Davis, recently conducted a two-part study to find out how muzzles affect social behavior and stress levels. Burk presented the results of their study at the 2019 Equine Science Society Symposium, held June 3-6 in Asheville, North Carolina.

How Grazing Muzzles Work

Grazing muzzles work by limiting a horse’s forage intake to what can be consumed through a small hole. Because they cover the nose and mouth, however, they can inhibit natural behaviors such as mutual grooming, facial expressions, and defensive biting. Therefore, said Burk, they might cause undue stress and have negative consequences on horses’ welfare.

The Study

In the first phase of their study, Burk and Davis used six mature Miniature Horses—a breed prone to obesity—turned out 24/7 in adjacent quarter-acre grass paddocks. They rotated two Minis at a time through three 21-day treatment periods: no muzzle, muzzled for 10 hours per day, and muzzled for 24 hours per day