Overweight horses: An increasing problem
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
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 carbohydrate intake.
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.