Feeding Metabolic Horses

Discover what, when, and how to feed horses with metabolic issues such as EMS, ID, and PPID.
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Feeding Metabolic Horses
Metabolic conditions affect horses’ ability to process soluble carbohydrates, including sugars and starches. | Photo: iStock

What, when, and how to feed horses with EMS, ID, and PPID

Every owner’s goal is to provide good care for their horse. But when your horse has a metabolic issue such as equine metabolic syndrome (EMS), insulin dysregulation (ID), or pituitary pars intermedia dysfunction (PPID, formerly called equine Cushing’s disease) or is overweight, good care takes on a whole new meaning. It boils down to what, when, and how to feed.

Horses with EMS have fat cells that produce a hormone that causes cortisol (which has a variety of functions, including regulating metabolism and immune response) levels in the body to increase. Although operating by a different mechanism, horses with PPID also synthesize more cortisol. As a result, the horse’s normal response to insulin is disrupted (e.g., insulin dysregulation). Horses with ID have high insulin and glucose concentrations circulating in their blood. When you add obesity to the quagmire, horses’ risk of developing EMS only increases. Horses with PPID or EMS are also at greater risk of developing ­laminitis.

Because each of these conditions affects horses’ ability to metabolize soluble carbohydrates, including sugars and starches, developing appropriate feeding strategies is of paramount importance for their welfare. Many owners of metabolic horses do not know how many calories these individuals need and how much feed and forage will provide that amount, says Paul Siciliano, PhD, professor of equine nutrition and management at North Carolina State University, in Raleigh. Putting together a balanced ration designed to target an appropriate energy intake—a neutral energy balance where intake equals expenditure—is one key to understanding what to feed your horse.

Because researchers have shown that increased adiposity (fat) can lead to metabolic issues in some horses and ponies, you’ll want to keep a close watch on your horse’s body condition. A body condition score (BCS) of 4 to 6 on the 1-to-9 Henneke scale is ideal. When you have a horse that scores 7 or higher, you might be looking at your first clue that you need to adjust his caloric intake.

What To Feed

Metabolic horses need to consume diets low (less than 15% of the total diet) in sugars and starches, says Amy Parker, MS, PhD, an equine nutritionist and technical services manager at McCauley’s, in Versailles, Kentucky. Avoid feeding them typical grains (e.g., oats, corn, barley) and added sugars (e.g., molasses), which are all high in starch and sugar. 

Most horses that we consider easy keepers—meaning they can maintain a healthy to heavy body condition on forage alone—need only a ration balancer that provides the required vitamins and minerals without adding more calories, plus a high-quality ­forage.

If a metabolic horse needs additional calories that forage alone can’t provide, consider feeding concentrates that are low in soluble sugars (below 10%) and high in digestible fibers such as beet pulp or soybean hulls. You can also augment calories by adding fat to the diet (e.g., vegetable or rice bran oil). Fats are energy-dense, providing 2.25 times as much energy as the same amount of carbohydrates.

Note that you can find sugars and starches in not only grains but also forage (pasture and hays). Siciliano says we might be underappreciating pasture’s caloric value—even a field that doesn’t look green and lush and is closely grazed can provide excessive calories to a horse that does not need them. Those blades of grass left close to the ground still contain quite a lot of carbohydrates. While pasture is an excellent calorie source for horses, it can be difficult to manage pasture intake in horses with metabolic issues. 

Feeding Metabolic Horses
Turning horses out to graze very early in the morning when the sugar content is lowest (about 4 a.m.) and bringing them in before the sugar content rises (by 10 a.m.) is a labor-intensive but effective method for limiting grazing. | iStock

When To Graze

Grazing horses can eat roughly half of their daily caloric requirements in three to four hours. Therefore, you’ll need to eliminate or closely control your metabolic horse’s pasture intake. One method is to turn the horse out when grass sugars are low. These decrease several hours after sunset each day because the plants use them as fuel to grow at night. So turning horses out to graze very early in the morning when the sugar content is lowest (about 4 a.m.) and bringing them in before the sugar content rises (by 10 a.m.) is a labor-intensive but effective method for limiting grazing. You’ll have to consider other issues, however. For example, if the temperature drops overnight to below 40 degrees Fahrenheit, then the plant’s sugars will still be high in the early morning because they did not get used. In addition, horses might become aware of their limited turnout and gorge graze, consuming even more calories than they generally would. If you’re going to use this method effectively, make sure you understand pasture plant metabolism and its changes with temperature, sunlight, and season.

Parker says you can also use a grazing muzzle. This allows the horse to take in fewer calories, sugars, and starches while still moving around and foraging. Grazing muzzles can limit intake by as much as 80%. She points out, however, that the muzzle must be used appropriately—the access hole should be small enough to only allow the horse to consume small amounts. An alternative is to turn the horse out in a drylot, where he can exercise without unfettered grass access; you control the amount of forage he gets.

Types of Forage

The type of forage intake you can control best is hay, which should be these horses’ main calorie source. Siciliano and Parker agree that you should have your hay analyzed to determine its nonstructural carbohydrate (NSC) content, which should be less than 12% for metabolic horses. Siciliano cautions, however, that owners should understand how to use this information when feeding their horses. For example, if a horse consumes 10 kilograms (22 pounds) of hay that contains 12% NSC, then he is consuming 1.2 kilograms (2.6 pounds) of NSC. However, if the horse consumes 8 kilograms (17.6 pounds) of hay that contains 15% NSC, he still consumes 1.2 kilograms of NSC. Focus on managing the caloric intake, which is what truly drives down NSCs.

Also consider hay type when feeding metabolically challenged horses. Cool-season grass hays (e.g., timothy, orchardgrass, bluegrass) can be relatively high in sugars, depending on when the grass was harvested. If the hay was cut when the sugar content was high, then the sugar and, thus, caloric content of that hay will be high compared to if the same grass hay were cut when the plant’s sugar content was low (e.g., first thing in the morning). Legume hays (alfalfa) are lower in soluble sugars but high in calories, so the issue with using legumes will be in adding calories, though not necessarily calories from soluble sugars. Warm-season grass hays (e.g., teff, some species of Bermuda grass) are naturally low in soluble sugars and, thus, make ideal hays for horses with metabolic issues.

Feeding a late-maturity hay is another way to reduce NSC levels. As plants mature, their amount of simple sugars goes down. However, other ­nutrients in the plant decrease too. So in feeding a late-maturity hay, you might have to add a vitamin/mineral or ration balancer to meet the horse’s nutrient needs.

Another option is to soak hay prior to feeding. Soaking hay up to 16 hours has been shown to reduce soluble carbohydrate levels by as much as 43%. It also reduces the nutrient and dry matter content and increases bacterial load. Therefore, be sure to feed soaked hay immediately to prevent mold and bacteria formation. The current recommendation is to soak the hay no longer than two hours, toss the water out, and feed the hay ­immediately.

Haylage is often presumed to have low NSC due to the fermentation involved in its production. However, haylage has been found to generate a higher insulin response than hay of an equivalent NSC content; therefore, researchers do not recommend feeding haylage to horses with metabolic issues.

What’s on the Horizon?

Scientists are currently exploring the metabolic phenotypes (genetic physical markers) of horses that have or might be prone to metabolic issues. Researchers at the University of Minnesota and Michigan State University are trying to determine if they can use genetic markers to confirm that certain horse breeds are prone to certain metabolic syndromes/diseases. Results of this research should help us better understand how to develop or adjust diets for at-risk horses.

Researchers are also currently looking at the microbial population in these horses’ guts. A team from the University of Montreal, Quebec, and the University of Guelph, Ontario, is investigating intestinal microbiome markers that might be associated with various disease states in horses. These study results might provide insight into parameters owners should consider when feeding their horses.

Take-Home Message

Because metabolic issues challenge horses’ health, Parker reminds owners to always seek professional advice when designing and tweaking diets. Select feeds based on your horse’s needs, and feed them properly. With horses prone to metabolic issues, says Siciliano, “stick to the basics of nutrition and feeding, and don’t let your horse get fat.”


Written by:

Debra Powell, PhD, PAS, is the owner of Powell Equine Canine Therapy Services LLC which offers nutritional consultations, pasture evaluations, feed formulations and complementary therapies for horses and dogs; author of equine digestive anatomy and physiology book as well as author of a chapter on equine facilities. Dr. Powell has published several scientific journal articles related to her field of research in equine exercise, obesity and insulin resistance in horses. She resides in Charleston SC where she spends time with her two retired Thoroughbreds.

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