Study: Do Grazing Muzzles Cause Stress?

by | 08.10.2019 | 4:43pm

While horses and ponies wearing grazing muzzles may look a bit like Hannibal Lecter, the apparatus serves an essential purpose: Limiting an equine's intake of grass so they don't become obese and prone to the potential harmful ramifications being overweight brings.

Grazing muzzles can reduce forage intake by between 30 and 83 percent, reports The Horse. While they do help slow down eating, they also cover a horse's muzzle and can mask some of his body language toward other horses, like mutual grooming and defensive biting. To determine if the muzzles were stressful to the horses wearing them, Dr. Amy Burke of the University of Maryland conducted a two-party study. She presented her findings at the 2019 Equine Science Society Symposium.

The study used six Miniature Horses that were turned out 24/7 on quarter-acre lots in groups of two. The study covered three, 21-day study periods, where the equines were muzzled for 24 hours a day, not muzzled at all or muzzled for 10 hours a day. Video was taken of the Mini's behavior twice a week and their body condition score, girth circumference, weight and cresty-neck score were recorded before and after each trial period. Additionally, how the Mini's accepted the muzzle was noted, as was their heart rate and salivary cortisol levels, both of which are indicative of stress.

The Horse reported that the study revealed that:

  • Muzzled Minis had no stereotypies or frustration behaviors
  • Minis muzzled for 24 hours at a time lost weight, but had no other physiological changes
  • Minis muzzled for 24 hours grazed more than other Mini's in an attempt to get more grass
  • Minis muzzled for 24 hours had lower heart rates and greater heart rate changes than the others Minis
  • Minis muzzled for 10 hours rested more and grazed less than the other two groups
  • Unmuzzled Minis spent more time mutually grooming than muzzled Minis

Interestingly, there was no difference in salivary cortisol levels between the groups.

The next part if the study housed the Minis together in a 1.4-acre field to see how the muzzles affected their exercise, weight loss and hierarchy. All recordings were completed again and a GPS tracker was added, showing that the Minis traveled nearly 4 miles per day as a herd.

It was determined that  Minis that were muzzled for 24 hours stood the most, while the unmuzzled Minis trotted and cantered the most. Unmuzzled Minis groomed themselves the most. Interestingly, though muzzled Minis couldn't bite, the dominance rank didn't change.

The researchers concluded that equines wearing grazing muzzles for 10 or 24 hours were not more stressed than unmuzzled horses, but their behavior was altered. They also suggested that wearing a muzzle may provide a cardiovascular benefit to the horses as constant foraging may have a calming effect, lowering heart rates.

Read more at The Horse.

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