Reduced pasture time: A good solution?
It seems fairly intuitive then that the best means of controlling a horse's carbohydrate intake is to limit its access to
pasture, especially lush green pasture. If you drastically limit a horse's access to green grass, so the thinking goes, then
you drastically reduce its intake and its chances of overeating.
Paul Siciliano, a PhD nutritionist in the Department of Animal Sciences at North Carolina State College of Veterinary Medicine,
recently presented new information at a nutritional short course that calls this reduced pasture time theory into question.
Siciliano's work showed that if you reduce the pasture time available for grazing by a particular horse, then that horse generally
responds by increasing its grazing intake, so the overall carbohydrate consumed is roughly equal. Some exceptionally motivated
horses in Sicilano's study were able to consume 17 hours' worth of grass intake in only three hours of turnout, assuming that
quantity was not limited. Thus, simply limiting turn out will not work.
Another option for controlling overweight horses in the spring grass season is to limit intake, and the equine grazing muzzle
makes that approach possible. Grazing muzzles greatly reduce the bite size that horses can take, and they make individual
horses spend a greater proportion of time engaged in foraging behavior (more walking, less eating).
A recent study conducted in Wales, U.K., showed that pasture intake by ponies wearing muzzles was only 0.14 percent of body
weight over three hours, which amounts to an 83 percent reduction compared with non-muzzle-wearing horses.4
Another study by Tracey Hammond, a nutritionist for Dengie Feeds, demonstrated a restricted grass intake with a grazing muzzle
of 75 to 86 percent. "Muzzled horses had a 50 percent reduction in bite depth and a 62 percent reduction in bite weight, which
is likely to provide the strongest evidence for how and by how much a muzzle restricts intake," says Hammond. Horses wearing
a muzzle simply cannot bite as deeply or get as big of a bite as horses that are not wearing one.
There are many different designs for grazing muzzles, and proper, comfortable fit is important. Most manufacturers recommend
that muzzles remain in place for no longer than 12 hours at a time.
"Grazing muzzles appear to be an effective method of restricting pasture intake," says Clare Barfoot, one of the researchers
of the study on muzzle use in the U.K. "The study has given us helpful, practical guidance on how we can safely manage grass
intake to control weight gain and reduce the risk of obesity-related disorders, without significantly compromising the natural
behavior and wellbeing of our horses and ponies."
When it comes to spring green grass, it truly is a case for "less means more," and a well-fitting grazing muzzle may be the
Dr. Marcella is an equine practitioner in Canton, Ga.
1. Thatcher CD, Pleasant RS, Geor RJ, et al. Prevalence of obesity in mature horses: an equine body condition study. J Anim Physiol Anim Nutr 2008;92(2):222.
2. Stephenson HM, Green MJ, Freeman SL. Prevalence of obesity in a population of horses in the UK. Vet Rec 2011;168(5):131.
3. Asai Y, Matsui A, Osawa T, et al. Digestible energy expenditure in grazing activity of growing horses. Equine Vet J Suppl 1999;30:490-492.
4. Longland A, Harris P, Barfoot C. The effect of wearing a grazing muzzle vs. not wearing a grazing muzzle on pasture dry matter
intake by ponies. J Equine Vet Sci 2011;31(5):282-283.