How to Feed Horses With Metabolic Challenges

A brief overview.

Originally published in the September 2015 issue of Veterinary Practice News

Most horses’ nutritional requirements are satisfied by having enough good hay to fulfill their caloric needs, water and a salt block (probably). 

But it is increasingly recognized that certain equine metabolic conditions can benefit from special diets targeted toward specific aspects of the condition. Recognizing that a horse has a metabolic problem is usually not particularly difficult, as horses will often show stereotypical clinical signs. 

Here’s a brief overview of a few common conditions and nutritional strategies that may help address them.

Insulin Resistance/Equine Metabolic Syndrome (EMS) in Equines

EMS is a problem in both horses and humans. Horses with EMS become less sensitive to insulin’s effects, and more insulin than normally required is needed to keep blood sugar concentrations within normal limits, especially after a meal high in starch or sugar.

The cause of EMS is not known, but a genetic component may be involved. Since these horses usually require relatively little feed to maintain their weight, they are commonly referred to as “easy keepers.”

Unregulated insulin-resistant horses get fat and typically deposit fat in areas such as the crest of the neck or over the tail head. They often maintain their fat even when the rest of their body appears relatively thin. Nutritional management of EMS horses includes:

  • Maintaining good body condition. The ribs should be easily felt but not easily seen. 
  • Avoiding or limiting pasture grazing in the spring and fall when grasses are growing rapidly, have less fiber and contain more sugar.
  • Feeding hay with low levels of sugars (soluble carbohydrates). Moderate quality timothy or orchard grass hays are best. Oat and rye grass hays have more sugar than do timothy or orchard grass. Legume (alfalfa) is OK, but it has more calories than do grass hays, which can lead to obesity. Clover hay is high in sugar and should probably be avoided. 
  • Soaking hay in water for 15 to 60 minutes can help remove nonstructural carbohydrates.  Soaking for longer than 60 minutes can result in very low concentrations of carbohydrates, high calcium-to-phosphorus ratios, and a significant loss of dry matter. Many low-starch commercial feeds are available.
  • Using beet pulp and soy hulls, which have low sugar levels and may provide extra calories. Avoid grains. Adding fat is a good way to supplement calories. 
  • Avoiding supplements such as chromium or magnesium, which have been shown to be ineffective.
  • Promoting exercise. Most overweight horses don’t have insulin resistance; they’re just fat. However, exercise also helps insulin do its job. Of course, exercise is beneficial for all horses.    

One good source for EMS testing is Cornell University here

Hyperkalemic Periodic Paralysis

HYPP affects muscle cell membranes. It was first identified in descendants of the American Quarter Horse sire Impressive.  Hyperkalemia causes muscles to contract more readily than normal. Affected horses have sporadic episodes of muscle tremors or paralysis, depending on the severity of the problem. Veterinarians should advise clients to:

  • Avoid high-potassium feeds such as alfalfa hay, brome hay, canola oil, soybean meal or oil, and molasses.
  • Feed timothy or Bermuda grass hay, beet pulp, or grains such as oats, corn, wheat and barley.
  • Pasture is usually OK. The water content in pasture grass makes consuming excessive potassium difficult.
  • Feed several times a day.
  • Provide regular exercise.

One lab that offers testing for HYPP is the University of California Veterinary Genetics Laboratory here.

Tying Up/Shivers

Horses affected with polysaccharide storage myopathy (PSSM), tying up and shiversaffected horses look like they are having muscle cramps—have trouble metabolizing carbohydrates. The nutritional goal for these horses is to provide no more than 15 percent total daily calories from starch and sugar, and at least 20 to 25 percent of total daily calories from fat. 

Just about any kind of hay is OK. The key to nutritional management is to get fat into the diet, usually in the form of plant-based oils.

Oregon State University Professor Beth Valentine, DVM, Ph.D., has developed a diet for horses that can benefit from extra fat. Her specific dietary recommendations are here

The University of Minnesota has studied these conditions extensively and offers testing here


Laminitis, which affects horses’ feet, can result from many different diseases and is commonly seen in older horses with pars intermedia pituitary disorder (PPID, or equine Cushing’s syndrome). While no specific diet can reverse laminitis once it has started, low carbohydrate diets and weight loss are commonly recommended. 

Prevention is the key to avoiding laminitis. Horses should not be allowed to get fat, and their intake of easily digestible sources of carbohydrates should be limited. Tips for reducing carbohydrate intake include:

  • Limiting pasture. Almost 50 percent of all laminitis cases have been attributed to access to lush pasture. While pasture is great horse feed, the potential for laminitis can be reduced by barring horses until the grass is mature, limiting grazing time to a couple of hours a day, grazing in the afternoon—carbohydrates in grass peak in the middle of the day—and using a grazing muzzle.
  • Offering moderately good quality grass hay in addition to pasture, to provide a fiber source. 
  • Limiting access to whole or processed grains. Like lush pasture, grains are high in easily digestible carbohydrates and very low in fiber. Most horses don’t need grain and are better off without it.


Excessive fat is no healthier for horses than for other animals (or their owners). The ideal body condition for a horse is one in which you cannot see the ribs but can feel them easily. Suggestions for controlling obesity include:

  • Increasing exercise.
  • Weighing feed. Feeding by flakes or buckets tends to give a horse too much to eat, and it is wasteful and expensive. For maintenance, a horse should get 1.5 to 2 percent of its body weight per day in feed. That’s 15 to 20 pounds for a 1,000-pound horse.
  • Substituting grass hay for legume hay. Grass hay has fewer calories, so horses can eat the same weight of feed, get fewer calories and keep their weight down.
  • Feed healthy treats. Carrots and watermelon rind have fewer calories than things like a pound of oats or molasses-soaked horse treats. 

Good nutritional management is an important part of helping a client to maintain a healthy horse. While a good diet can’t prevent or treat all conditions of the horse, it’s unquestionably important, and it’s not all that hard to provide. 

Certain metabolic conditions do benefit from a sensible approach to feeding. Good nutritional management doesn’t have to be expensive or difficult, and horse owners appreciate their veterinarian’s involvement.

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2 thoughts on “How to Feed Horses With Metabolic Challenges

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  2. My mare was Diagnosed with PSSM 1 when she was 8 years.. she was also suspicious of having Insulin Resistance and we treated her as such but was never tested . She is now showing symptoms of Cushings , long hair coat that doesn’t shed. Is it possible to have all three.. Symptoms are Easy keeper, low energy, long hair coat, She used to have chronic foot pain White line separation chronic abscesses but with corrected diet and a knowledgeable farrier this has helped tremendously.. We did have a vet who put her on Pergolide before she was diagnosed with PSSM years ago thinking it was Cushings then and it did nothing.. She was also on Insulinwise llast year and we saw no change.. We have just recently started her in Heiro. But it is too soon to tell. .. I did follow Dr Beth Valentines diet when she tested positive for PSSM 1 and now cringe to think if the high fat diet could of contributed to Insulin Resistance seeing she was already a easy keeper .. right now she is on a high natural vitamin E supplement, salt, MSM, and a joint supplement mixed with a small amount of balancer .. She is a Percheron/QH cross and is now 16 years old.. what else can I do to help manage her .. We use hay nets limit spring and fall pasture time and she is in light work .. Thank you Christine Oppedisano


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