Slimming Down

In this age of plenty it is not uncommon to see horses carrying too much body fat. Such an individual exceeds what we might call pleasingly plump; in other words, he is fat. When running your hands across the horse's sides, you won't feel any ribs beneath his flesh. Often a fat horse has developed a cresty neck, and if you can stand on a fence rail and peer down on him from above, an overweight horse might appear to have a "rain gutter" along his back. When the girth or cinch is tightened, it makes a distinct dent in the underlying flab. Some might think such a horse is solid and in full "bloom," ready for the show season ahead. But such a body condition is dangerous to the health and athletic future of the horse.

Where to Start?

Philip Johnson, BVSc (Hons), MS, MRCVS, Dipl. ECEIM, professor of veterinary medicine and surgery at the University of Missouri, has explored hormonal aberrations that result from overfeeding, particularly as related to what he describes as equine metabolic syndrome (EMS). His recommendations to treat the problem of obesity are based on common sense and a healthy approach to dietary management. First, an owner must recognize that a horse is, in fact, overweight or obese. He urges, "To improve metabolic health, a philosophical shift is necessary. An acceptable and desirable body condition, as perceived by a horse owner, should be a horse that is fit and trim."

Johnson suggests using measurements with a weight tape and with body condition score (BCS) to evaluate how your horse measures up to ideal body weight. Then he urges owners to implement a sound nutritional program in consultation with a veterinarian.

A starting place in feeding an overweight horse is to take a realistic look at what your horse has previously been ingesting. Sometimes it is easy to think that a horse in a herd is only eating a specified amount when, in fact, he might be driving others away from their feed and consuming a double ration. In that case, it is important to isolate the horse during feeding time so there is no question about how much he eats.

Restricting calories is key to success--if your fat horse has previously been on pasture, put him into a dry paddock with restricted access to measured portions of food or confine him to a portable pen that can be moved around the pasture to restrict grazing, or attach a grazing muzzle to a breakaway halter.

How Much and What to Feed?

The next step is to critically evaluate exact amounts and types of material fed. The only accurate way to determine this is to weigh the ration with a feed scale.

" 'Guesstimating' how much something weighs is fraught with error and limits how well you are able to fine-tune the diet," states Johnson. "Getting an accurate weight on your horse is invaluable. A lot of people take their horse to the feed distributor and weigh the horse and trailer at their weigh scale, then weigh the trailer empty the next trip to town." Weight tapes can be used, but they are rough estimates geared to measuring adult light horse breeds.

As a general rule, most horses consume about 2% of their body weight each day for maintenance, with a 1,000-pound horse getting along fine on a daily ration of 18-20 pounds of grass hay. To assist a fat horse in losing weight, you might need to cut his hay back to a total of around 15 pounds for the day.

Johnson remarks, "It's important to feed to a desirable target weight. Your veterinarian should evaluate the horse's current weight and body condition score (BCS) and make a recommendation as to what the weight and BCS should be. Different breeds and types may have different standards." 

All recommendations should be in conjunction with the caloric content of the hay based on lab analysis, when possible.

In concocting a dietary plan, Johnson recommends, "Remove as much grain and supplement feed as possible, including complete or senior feeds containing high starch or sugar." In most cases of a fat horse, you need offer nothing more than hay, salt, and water.

Concentrate feeds, especially with those that are carbohydrate-rich, elicit large surges in blood glucose. In response, insulin hormone concentrations peak to facilitate storage of glucose as glycogen in the muscles and liver. Obese horses are often insulin-resistant, which means higher amounts of insulin are released in response to a standardized sugar or starch challenge than is considered to be normal (hyperinsulinemia). Their blood glucose might or might not be elevated, too (compensated or uncompensated insulin resistance, respectively). Hyperinsulinemia has been associated with increased risk of laminitis.

The average mature horse only needs 8-10% protein in his ration. Feeding a higher percentage of protein adds unnecessary calories to the diet. The most important component of a horse's diet to provide is plenty of forage for fiber. Horses thrive best on a high-fiber diet of hay and/or nonirrigated pasture as main ingredients.

Legume hays, such as alfalfa, are much higher in calories and protein than grass hays. In some cases, up to 10-15% alfalfa in the diet might be relatively safe, but Johnson remarks that for unknown reasons, some insulin-resistant horses do not tolerate legume components in their diet, responding adversely either by not losing weight and/or by developing laminitis.

If your horse eats everything placed in front of him, you'll have to control his intake. Your objective is to offer good-quality grass or oat hay rather than legume hay. (Be aware that oat hay can be extremely high in calories and starches if harvested properly.) Offer 1.5% of the horse's body weight in moderate-quality grass hay, and, using the weight scale, divide it into three or four feedings per day.

You might be fortunate to have abundant pasture available for your horse, yet for an obese horse, this is not a good thing. Pasture grasses can be high in sugar, starch, and/or fructans (all of which are collectively called nonstructural carbohydrates, or NSC), especially during periods of rapid growth or occasions when the plants are stressed by frost, drought, or overgrazing conditions.

In the presence of sunlight, through photosynthesis, all growing plants accumulate high-calorie sugars and starches that are then converted to low-calorie fiber or structural components at night if the temperature is above freezing and there is adequate water. Therefore, if the temperature is above freezing and there has been adequate rainfall, the safest time to graze an obese, founder-prone horse is in the early morning hours (pre-dawn to about one or two hours after the sun has come up). However, if it freezes overnight or it has not rained for a long time (i.e., grasses are starting to dry up), keep your fat horse off the pasture.

Hay might also contain fairly high NSC, depending on how and when it was harvested. For the most accurate assessment of NSC content of hay, submit a sample for laboratory analysis. (One useful resource for feed analysis is Dairy One laboratory in Ithaca, N.Y.;; 800/496-3344.)

In addition to dietary restrictions, the fat horse should have plenty of exercise. Longeing, or even just chasing the horse around the pasture once or twice a day for 10 minutes or so, will help him trim down if you do not have time to exercise him regularly.

Timing of Weight Loss

Johnson notes that a horse should shed pounds slowly over the course of several weeks to months (accomplished with the supervision of a veterinarian). "Forage intake should be decreased accordingly at a rate of 10% per week, yet forage intake should not be less than 1.25% of body weight per day," he says.

A safe general rule is to provide about 70% of a horse's calculated daily ration to achieve safe weight loss. (For example, a 1,000-pound horse that might normally consume 20 pounds of hay per day would receive 14 pounds total ration for the day. In keeping with the safety margin of 1.25% of his body weight, under no circumstances should he be offered less than 12.5 pounds of hay per day.)

Starvation through severe calorie restriction is a metabolic stressor, especially in cases where a fat horse develops hyperlipemia syndrome (elevated levels of triglycerides or storage fats), leading to liver failure and slow metabolic rates. Such severe fat mobilization, also known as fatty liver disease, is particularly a risk for insulin-resistant, obese ponies and Miniature Horses.

Johnson also cautions, "If the roughage is reduced too much, a horse tends to become 'stir crazy' and may develop stable vices such as eating wood in the stalls or paddocks, in addition to being more prone to colic and gastric ulcers."

If good-quality hay is difficult to find, one reasonable fiber supplement that can be substituted for a portion of the hay ration is beet pulp, provided it does not contain molasses. Beet pulp maintains a horse's glycemic response at a steady level, without vast fluctuations as seen with grains. For each pound of beet pulp (dry weight) fed, Johnson suggests eliminating 1.5 pounds of hay from the diet. He also recommends feeding certified low-NSC complete pelleted feeds to ensure minimal intake of feed with high sugar content.

An additional suggestion from Kathyrn Watts, BS, of Rocky Mountain Research and Consulting, helps reduce the NSC content of hay. All you do is immerse the hay in warm water for an hour prior to feeding. Soaking dissolves soluble sugars that are then thrown out with the water before feeding. Some veterinarians caution this is not necessary for most hays and also leaches out the potassium.

If your horse needs oral medication and you're trying to reduce his calorie intake, try mixing it with a small amount of beet pulp mash or soaked pelleted feed that is low in fat (less than 5%) and high in fiber (more than 15%). Or, mix powders with unsweetened applesauce and give them by oral dose syringe. Avoid sweet feeds and grains.

Johnson adds, "A veterinarian should check a fat horse's health before implementing a slimming program." He recommends a thorough physical exam and possible blood tests to screen for hormonal aberrations. Then, regular evaluations are made during the weight loss program to compare to the initial clinical findings.

Weight Loss for Laminitic Horses

The obese horse with laminitis certainly presents a challenge to the person designing a weight reduction program. All grain and calorie-dense supplements should be eliminated from his diet. In addition, Johnson notes, "For reasons that are as yet incompletely understood, alfalfa should be avoided--it appears to be a risk factor for laminitis in and of itself."

Johnson laments that laminitis is a problem from the perspective of increasing exercise; there is not an easy way around this problem. Increasing exercise is important in weight loss programs, but it's not practical when a horse is suffering from severe musculoskeletal pain. Anything that reduces stress is important for improving such a horse's metabolic state, since stress elevates levels of glucocorticoids that promote insulin resistance. Laminitic pain exacerbates stress and increases insulin resistance, making this a nonending cycle of events.

Laminitis prevention is the best cure. Johnson feels this is best achieved through recognizing the significance of obesity and unhealthy feeding programs, along with recognizing early subtle, preclinical signs of laminitis, as seen with abnormal hoof growth, broadening of the white line zone, and dropping of the sole.

Feeding Recommendations

The key to weight loss and a slimming diet is moderation and careful thought. A fat horse becomes fat because of overfeeding, particularly a diet rich in carbohydrates or grain and energy-dense feed. To assist your horse in safe weight loss, consider these general rules:

  • Consult with your veterinarian to tailor a diet specifically for your horse based on physical exam and laboratory results.
  • Your veterinarian can perform specific endocrinological tests that will help ascertain whether an individual horse is at risk for insulin resistance.
  • Provide high quality forage, preferably grass hay that is low in nonstructural carbohydrates and sugars.
  • Avoid legume products when possible.
  • Offer a fat horse about 70% of what his hay ration would be if he were in normal body condition on a maintenance diet.
  • Find a way to accurately get a weight on your horse and weigh all food offered.
  • Eliminate all grains and excess carbohydrates (other than those found in hay) from the diet.
  • Do not feed any of the following, which are rich in sugars: Molasses, carrots, apples, green grass, or complete feed products that are not certified low in NSC.
  • Split the daily ration into three to four feedings when possible to prevent long fasting intervals, relieve boredom, prevent stall vices, and to protect against gastric ulcers and colic.
  • Minimize extraneous feed additives and minerals, feeding only what is necessary to constitute a balanced ration.
  • Have feed and hay analyzed by a laboratory to obtain specific nutrient content, especially of soluble carbohydrates.
  • If necessary and practical, soak hay in warm water an hour before feeding, then drain off and discard the water to remove dissolved carbohydrates.
  • Exercise or provide regular turnout as often as possible, and implement a steady conditioning program.
  • If any grazing is allowed, turn the horse out only for short periods around dawn, when the plants are growing without environmental stress.
  • Turn the horse out with a grazing muzzle to restrict grass pasture intake, taping off the hole in the grazing muzzle as much as necessary.

Take-Home Message

Consistent exercise should be coupled with controlled intake of food and calories, along with minimal intake of nonstructural carbohydrates and sugars. Johnson urges, "Exercise is more important than diet when it comes to both losing weight and being healthier!"


You might be familiar with the easy keeper with the cresty neck and fat pads over the shoulders, back, and rump. A male horse might habe a thickened prepuce from fat deposits in that location. When scored on body condition, such a horse is considered fat or obese. In many cases, a fat horse might be affected with equine metabolic syndrome (EMS). Obesity in horses is often created by human factors, as a result of overfeeding or not restricting a horse's access to abundant and/or rich food. A fat horse is not just fat on the outside; he forms fat inside as well, particularly within the omentum (the membrane lining the abdominal cavity) that covers the bowel and within liver or fat cells in the abdomen. Fat cells are responsive to endocrine signals; the more fat cells present in the abdomen (as occurs with obesity), the greater the risk of hormonal irregularities. Enzyme activity in these intestinal sources of fat elicits high levels of circulating corticosteroids.

Historically, a fat horse was often diagnosed as being hypothyroid (thyroid hor-mone-deficienct), but usually this wasn�t the primary problem. The hormonal upset is not within the thyroid gland, but, rather, it is due to irregular hormonal feedback in the entire body as a result of high levels of corticosteroids.

A secondary consequence might be some degree of diminished thyroid hormone levels, but it is the fat as an organ that is creating the hormonal imbalances.

With high levels of circulating corticosteroids comes insulin resistance (IR), in which the body is unable to remove high levels of ingested glucose from the bloodstream and send it to normal storage repositories in the liver and skeletal muscle. Solving the obesity problem is essential to normalize a horse�s hormonal system and to prevent laminitis, improve wound healing, and improve general health.

Philip Johnson, BVSc (Hons), MS, MRCVS, Dipl. ECEIM, professor of veterinary medicine and surgery at the University of Missouri, remarks, "Thyroid replacement therapy with levothyroxine sodium (synthetic thyroxine, which increases the metabolic rate of cells of all tissues of the body) could be administered to morbidly obese horses or ponies, or those with strong evidence for significant IR, as an adjunct to the obesity-reducing ration and exercise program. Such treatment should be done in concert with appropriate veterinary supervision. Electing to use thyroid supplementation for weight reduction should not be done because of an inaccurate diagnosis of hypothyroidism, and it should not be a lifelong commitment. Its use is to help achieve temporary weight reduction and to improve insulin sensitivity."

The solution to obesity problems is not achieved through prescription medication, but rather through diligent and careful nutritional planning for a weight loss diet. --Nancy Loving, DVM

About the Author

Nancy S. Loving, DVM

Nancy S. Loving, DVM, owns Loving Equine Clinic in Boulder, Colorado, and has a special interest in managing the care of sport horses. Her book, All Horse Systems Go, is a comprehensive veterinary care and conditioning resource in full color that covers all facets of horse care. She has also authored the books Go the Distance as a resource for endurance horse owners, Conformation and Performance, and First Aid for Horse and Rider in addition to many veterinary articles for both horse owner and professional audiences.

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