Grazing Muzzles' Efficacy at Reducing Pasture Intake

While British artist Norman Thelwell’s depictions of pleasantly plump ponies make most horse lovers crack a smile, actually owning a horse with this body type is serious cause for concern. Equine obesity can lead to a variety of sometimes life-threatening ailments including laminitis and equine metabolic syndrome.

The challenge facing these horses’ owners is an effective method by which to restrict the amount of pasture or hay these animals consume. Many owners turn to grazing muzzles to reduce horses’ forage intake, and a group of British researchers recently determined this method can be very effective.

Annette Longland, BSc, PhD, CIBIOL, DIC, head of equine research at Equine and Livestock Nutrition Services in Wales, U.K., presented findings from a recent study evaluating the efficacy of grazing muzzles on ponies at the 2011 Equine Science Society Symposium, held May 31-June 3 in Murfreesboro, Tenn. Accompanying Longland on the research was Patricia Harris, MA, PhD, Dipl. ECVCN, VetMB, MRCVS, of the WALTHAM Equine Studies Group in England.

“Anecdotally, ponies fitted with grazing muzzles spend a greater proportion of time engaging in foraging or eating behavior than their nonmuzzled counterparts, yet either lose weight or retain an established, trim body condition,” the researchers explained. “However, there is little information on the extent of intake restriction imposed by grazing muzzles.”

The team studied four adult ponies either grazing freely or with a well-fitted grazing muzzle for “four three-hour occasions per pony” (a total of eight measurements per pony were taken). Each muzzle had a 2 cm diameter hole through which the ponies could eat.

Researchers obtained pasture samples daily to assess the amount of forage available to the ponies, and they determined each pony’s insensible weight loss (ISWL, the loss of body weight not associated with the loss of feces and urine; often associated with fluid loss from respiration and sweating) immediately preceding and immediately following each three-hour grazing period. Pasture intakes were determined by changes in body weight (after taking into account the weight of any feces and urine produced plus the estimated ISWL) after the three hours of grazing, using a calibrated weighbridge.

Upon reviewing results, the team found that:

  • On average, a properly fitting grazing muzzled significantly reduced the amount of dry matter consumed by about 85% as compared to ponies grazing without a muzzle;
  • Without a muzzle, ponies consumed an average of 0.8% of their body weight in three hours (with some eating close to 1%), which is equivalent to between a half and two-thirds of the recommended daily dry matter allocation for many horses on restricted diets; and
  • The grazing muzzle reduced average dry matter intake to around 0.14% of bodyweight over the three hours.

“Grazing muzzles appear to be an effective means of restricting pasture intake by ponies,” the researchers concluded.

Grazing muzzles must be used with care, should be properly fitted, and horses and ponies should be adapted gradually to wearing them.

“(A well-fitting grazing muzzle is) one that stays on the pony and also one that does not cause hair loss or abrasion to the skin through rubbing or restrict jaw movement (i.e., chewing) in any way,” Longland explained.

She also noted some other considerations owners should be conscious of when introducing a muzzle:

  • Acclimatize the pony to wearing the muzzle for short periods, gradually building up to the allotted total grazing time;
  • Be aware that muzzled ponies cannot display normal defensive behavior with their mouths, so keep an eye out for trouble … with mixed groups of muzzled and nonmuzzled ponies;
  • Some ponies sneeze a lot when a new muzzle is put on, possibly due to the smell of the new rubber at the base of the muzzle. The sneezing soon wears off as does the new rubber smell;
  • Make sure the pony realizes he can drink through the muzzle; and
  • Use a muzzle with safety ‘breakaway’ straps so the pony can escape should he become caught up in anything.

Longland and Harris added that owners should closely monitor group and individual behavior to observe any potential concerns caused by changes to the herd dynamics. They do not advise using total exclusion muzzles, which prevent any forage intake.

“Be vigilant and see what works for your pony,” Longland concluded.

The abstract, “The effect of wearing a grazing muzzle vs not wearing a grazing muzzle on pasture dry matter intake by ponies,” was published in the May/June issue of the Journal of Equine Veterinary Science.