The Dieting Horse

Too bad there isn’t a motivational weight loss "spokesmare" to help us out.

When you see two mares standing side by side facing opposite directions, do you ever think they might be checking out each other's rumps, saying, "No, of course I don't think that blanket makes you look fat." Or perhaps that high-strung, nervous mare isn't really nervous. Instead, she is berating herself constantly, saying, "I just shouldn't have eaten that last blade of grass! Or that one ... or that one ... "

This is probably a bit of a stretch on the anthropomorphism front; however, weight management is an important issue in equine medicine, particularly as more details on the underlying mechanisms of metabolic syndrome and insulin resistance surface.

In 1998 the USDA estimated approximately 1.4% of the horse population was overweight or obese. A more recent study, however, found the number of overweight or obese horses to be alarmingly higher.

"In a subpopulation of horses in Virginia, we found that 51% were overweight or obese," relays Craig Thatcher, DVM, PhD, Dipl. ACVN, department head of large animal clinical sciences at the Virginia-Maryland Regional College of Veterinary Medicine, in a study abstract published in a 2008 edition of the Journal of Animal Physiology and Animal Nutrition.

If these results are representative of horses throughout the United States, then the occurrence of obesity in horses is quite alarming.

Assessing a Horse's Weight

Owners should critically evaluate their horses' body condition frequently to target obesity before it takes hold. "At the University of Kentucky we use the Henneke Scale," explains Fernanda C. Camargo, DVM, PhD, an assistant professor and equine extension specialist in the University of Kentucky College of Agriculture's Animal & Food Sciences Department. "Using this scale, a horse is considered fleshy with a BCS of 7, fat with a BCS of 8, and extremely fat with a BCS of 9. A horse with a BCS between 4 and 6.5 is acceptable for most disciplines. Above 7, horses are considered fat."

The BCS is described in detail in the special report, "A Better 'Weigh' " (

"No horse should have a BCS of 8 or 9. An optimal BCS for a horse is typically 5-6. Even a pregnant mare should have a BCS of about 6," emphasizes Camargo.

According to Camargo, horses need to lose approximately 50 pounds to change one point on the scale. This decrease in BCS could take a couple of months to achieve, which highlights the importance of ongoing BCS assessments.

Girth tapes also are available to monitor body weight, but experts agree that BCS is the best way to monitor a horse's body weight--or, more accurately, his fatness or thinness.

The Perils of Pudge

The skyrocketing prevalence of equine body weight issues is a major concern. Philip J. Johnson, BVSc, MS, Dipl. ACVIM, Dipl. ECEIM, MRCVS, a professor of equine medicine and surgery at the University of Missouri College of Veterinary Medicine, notes, "Obesity represents a significant detriment to the health of horses in a manner similar to that by which it is affecting the human population.

"Contemporary husbandry practices embrace the provision of an energy-rich food ration to physically inactive domesticated horses," he explains.

What's worse is many owners are either unfamiliar with what an appropriate BCS in horses looks like, or they feel that a degree of obesity is normal, acceptable, and even desirable.

Horses' current lifestyles also are substantially different than their ancestors'.

"The equine species evolved as a free-roaming herbivore that walked great distances on a daily basis, paying heed to potential predators, in order to find and ingest a sufficient and suitable quantity of forage," notes Johnson. "In addition, evolution provided the horse with a metabolism that was best suited to its natural lifestyle before the influence of man-made domestication. Domesticated horses tend to be physically inactive and are provided with rations that are characterized by excessive dietary energy from the perspectives of both forage and grain."

Achieving a Healthy Body Weight

Contrary to common perception, most horses do not need grain as long as they are eating good-quality hay and don't have a high-performance routine.

"Owners like to grain their horses ... they are pretty much killing these horses with kindness," laments Camargo.

According to Camargo, weight loss in horses can be achieved by making two key management changes:

Reduce caloric intake Owners need to feed their horses less to reduce the number of calories consumed. Calories can be reduced by substituting lower-quality grass hay for the same amount (weight) of higher-quality hay.

"Try to avoid alfalfa and other legumes because they are very nutritive, and overweight horses do not need the amount of calories that alfalfa provides," advises Carmargo. "At the same time, do not feed your dieting horse straw or he could develop colic issues."

Camargo adds, "The term 'lower-quality hay' does not mean that the hay is a poor quality. Lower-quality hay is not molded. I simply mean hay that is lower in calories." You can have your hay tested to determine its nutritive value.

By switching to lower-quality grass hay and eliminating grain (or other concentrated feeds such as sweet feeds), you reduce the starch and sugar content in the horse's diet.

In addition, owners need to decrease or eliminate access to pasture. Grass provides a lot of sugars, and horses eat however much they want when they have free access. Try fencing off part of the paddock or field to make a drylot, and keep overweight horses in the drylot. If this is not possible, then using a grazing muzzle could be a reasonable alternative.

Ensure that you make all dietary changes slowly to avoid any untoward health issues (primarily colic).

Increase exercise level In concert with dietary changes (i.e., caloric restriction), most overweight horses also require an increase in their exercise level. For example, longeing or riding horses for 30-45 minutes a day at the trot is likely sufficient.

That being said, owners must be cognizant of their horse's current fitness level; if they are suddenly taking their horse from a sedentary life to an active one, they must start slow. Try riding or longeing at the walk for 10 minutes each day for a week, then increase the activity level thereafter until you reach your target.

Despite the decreased caloric intake and increased exercise regime, some horses will hang tight to their pounds. These horses could have an underlying medical condition. An examination and consultation with your veterinarian is likely indicated for these horses.

Exemplar Weight Loss Diet

A healthy adult horse requires 2-2.5% of his body weight in hay and forages per day. For an average 1,000-pound horse, this translates to about 20-25 pounds of hay in a 24-hour period. For an overweight mature, healthy horse, you can feed between 1-1.5% of his body weight in hay per day (10-15 pounds of hay). It is not recommended, regardless of how overweight a horse might be, to dip below 1% of his body weight in forage. For an average 1,000-pound horse, 10 pounds of hay is the bare minimum you should feed.

An easy keeper (a horse that is more metabolically efficient) requires approximately 15.2 megacalories (Mcal, equivalent to 1 million calories--not to be confused with the Calories [capital C] counted in human food, which are equivalent to 1,000 calories) per day to maintain his weight. Choose lower-quality mature grass hay, which has approximately 0.78 Mcal per pound, for this easy keeper (avoid alfalfa or immature harvest grass hay that has more energy [Mcal] per pound). This type of horse requires 20 pounds of a lower-quality grass hay to provide the required 15.2 Mcal. Since we want to achieve weight loss, we need to provide fewer Mcal--approximately 4 Mcal less every day.

If we were to feed higher-quality hay that provides more Mcal per pound, then we'd need to feed even less hay for our easy keeper to lose weight. This is not an ideal situation because if the dieting horse eats his smaller ration too quickly, he could become bored with extra time on his hooves and partake in inappropriate behavior. This highlights the need for owners to actually weigh their hay. For more information on hay analysis and weighing hay, visit

For advanced nutrition care, horse owners are encouraged to consult their veterinarian and/or an equine nutritionist.

Take-Home Message

The consequences of obesity in horses should not be underestimated; however, more research is needed to fully explore the impact and complications of obesity in domesticated horses.

"Whereas humans make their own nutritional choices, obesity in animals is always a direct consequence of management decisions made on their behalf by animal owners," notes Johnson.

In addition to the health implications, there is also a financial aspect that owners should consider when feeding their sure-footed friends.

"Provision of a healthier ration for horses would represent a considerable cost saving for owners who often expend con-siderable financial resource on rations that far exceed the horse's nutritional requirements," concludes Johnson.

About the Author

Stacey Oke, DVM, MSc

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

Stay on top of the most recent Horse Health news with FREE weekly newsletters from Learn More