It's that time of the year again—daylight savings time, tax time, time to deal with fresh spring grass pastures. And it's
time to deal with the problem of the overweight horse. This problem has been growing just about as fast as the girth size
of these "easy-keepers." And each spring, when carbohydrate-rich grass threatens to cause laminitis, metabolic syndrome flare-ups
and other obesity-related conditions, practitioners must do their best to keep things under control.
A look at the scale of obesity
The first study to look at the problem of the overweight horse was done in 1998 by the National Animal Health Monitoring System
for the United States Department of Agriculture, which estimated that roughly 5 percent of horses in America at that time
Time for the lush life: Spring grass is carbohydrate-rich and can make horses quickly pack on the pounds. (Photo courtesy
of Dr. Marcella)
A 2006 study undertaken at the Virginia-Maryland Regional College of Veterinary Medicine showed that, in eight years, that
number had skyrocketed to 51 percent, with 19 percent of those horses classified as obese.1 "The majority of horses in this study were fed primarily pasture and hay with very little grain or concentrate," reported
Craig Thatcher, a veterinary nutritionist who was one of the researchers.
A more recent study done in 2011 at the University of Nottingham in England found that nearly 54 percent of the horses examined
were overweight.2 This study showed that, again, most of these animals were maintained on grass and hay, proving that grain or concentrates
are not needed to produce an overfed horse and that pasture grass intake must be carefully regulated in order to realistically
manage body weight.
Walking the pasture: Sufficient exercise?
There is nothing inherently wrong with pasture grass for horses. But because horses are so good at grazing and today's grasses
contain such high amounts of carbohydrates, problems inevitably occur. The typical horse at pasture spends roughly 70 percent
of its time, or 17 out of every 24 hours, engaged in some form of grazing behavior. The remaining 30 percent is devoted to
sleep (one to two hours each day), play, socialization and various assorted herd behaviors. The type and quality of the pasture
greatly influences grazing time.
Raymond Geor, BVSc, MVSc, PhD, Dipl. ACVIM, of the College of Veterinary Medicine at Michigan State University explains that,
on average, 10 percent of a horse's day is spent walking at pasture looking for food. The poorer the pasture, the more time
spent looking for edible and palatable forage, so horses will spend less time grazing on a lush spring pasture than they will
on a mid- to late-summer pasture with poorer quality grass. This pasture quality difference translates, therefore, into a
difference in voluntary exercise as well.
Rather than being consistent with a work program of light riding, lunging or other exercise, clients often try to offer up
their horses' walking out on pasture as a method of controlling excess weight. It turns out that there is, in fact, some scientific
truth to this general wishful thinking after all.
Researchers at the Equine Science Division of the Hidaka Training and Research Center (a part of the Japanese Racing Association)
conducted a study in yearling Thoroughbreds and looked at the effects of grazing time on feed intake and energy expenditure.3 They found that horses that were allowed to graze for 17 hours daily on a 10-acre field travelled between 8 and 9.5 miles
and burned substantially more calories than horses allowed to graze for only seven hours on the same field. Those horses travelled
only 2.5 to 3 miles, with proportionally less energy expended.
While these distances walked and the energy used sound encouraging in principal, they must be counterbalanced by the effects
of grazing for that one-hour period because horses are quite capable of walking with their mouths full. When the actual numbers
are run, there turns out to be little overall benefit in dietary management achieved by leaving horses out on pasture for
extended periods. There certainly are other beneficial reasons for more turnout time (e.g., reduced colic, better joint health),
but we are speaking purely nutritionally in this instance. While all that excess walking around the pasture and grazing does
use up more calories, these horses also consume more calories eating for 17 hours straight. They actually end up with higher
Geor provides data supporting the fact that a horse at pasture 24 hours a day and grazing 17 hours out of that time will generally
consume up to 25 lb of forage. Since a mature horse needs to consume 2 to 2.5 percent of its body weight daily, this 25 lb
of forage is more than enough for maintenance needs. If this horse were to be fed any additional feed or concentrates, then
it would be overfed, and such management would be contributing to the problem of obesity.