EMS, Cushings, and Spring Feeding

by R. Paul Schwab, D.V.M

Over the next few months, our horses here in the Pacific Northwest will be challenged by the lush green grass we are blessed with after the months of rain and cold. For many, the grass is a welcome source of vitamins, protein, and carbohydrates and a break from relying on expensive hays and grains as a chief source of nutrition. For a growing number of horses, however, this same grass can be extremely dangerous to their health.

Equine Metabolic Syndrome and Equine Cushing’s Disease are two metabolic abnormalities of horses that make them extremely sensitive to the sugar content of lush, rapid-growing spring grass and sometimes any green grass at all.

Equine Metabolic Syndrome (EMS) is a syndrome in which horses are extremely “easy keepers” and seem to put on weight with barely any pasture. They tend to have more fat over the crests of their necks, around the tail head, and in the sheaths of geldings and stallions. There seems to be a breed disposition, with ponies, donkeys, Arabs, Paso Finos, and Mustangs commonly affected, although any breed is susceptible. Horses with EMS are more prone to laminitis (founder), as well. Veterinarians usually diagnose EMS when they are called out to see an overweight horse or pony that has laminitis.

One of the reasons these animals have such weight and laminitis issues is because of insulin resistance. In technical terms, insulin resistance describes a decreased response of tissues to insulin-mediated glucose uptake. Basically, there is plenty of insulin in the horse's system, but the muscles, liver, and fat tissues have only limited response to it. Insulin is responsible for telling the tissues to take up and use glucose, which is their main source of energy. In the case of insulin resistance, the glucose stays in the blood stream instead of going into the tissues, causing hyperglycemia (high blood sugar).

Over time, high glucose in the blood is toxic to the lining of the vessels and other tissues and contributes to the development of laminitis. High sugar/starch in the diet, or in some cases any sugar, overwhelms the metabolic ability of the horse to maintain the proper amount of glucose in the blood. The fat that accumulates on the crest of the neck, rump, and sheath may actually produce chemicals that worsen this insulin resistance.

Equine Cushing’s Syndrome is another disease in which horses are more sensitive to sugar in the diet. Equine Cushing’s Syndrome, or pituitary pars intermedia dysfunction, is a disease in which an enlarged pituitary gland in the brain causes a cascade of hormonal changes that ultimately result in an overproduction of cortisol. Cortisol is the body’s natural stress response hormone, which is needed during times of danger, stress, etc., but over time can result in damage to multiple organ systems. It brings down the overall immunity of the animal and causes insulin resistance. Horses with Equine Cushing’s Syndrome tend to have long, curly-haired coats that don't usually shed out in spring, drink and urinate frequently, and have problems keeping on weight. They are also extremely prone to laminitis.

Both of these conditions require diets with little or no starch or sugar. Sugar and starch are classified as Non-Structural Carbohydrates (NSCs). Examples of feed ingredients high in NSCs are corn, oats, barley, and molasses. These ingredients are low in fiber and high in sugar. Lush green grass can fall into this category because it is high in natural sugars called fructans. Ingredients low in NSCs include most hays and hay pellets, beet pulp, rice bran, soybean hulls, and oils. Knowing this information can help you formulate a proper ration for horses with EMS and Cushing's Syndrome.

Feeding Strategies
Obese Metabolic Syndrome Horse --Feed grass hay at the rate of 1.5-2% of their body weight per day (15-20 lbs. of hay per day for a 1,000 lb. horse). Yes, you really need to get into the habit of weighing your hay! Feeding a vitamin/mineral supplement is recommended because grass hay may not have the nutrition the horse needs. There are multiple commercial “super supplements” that have added protein as well that are ideal to feed to these horses. Don’t forget, these guys still need exercise. It helps the weight loss and encourages the tissues to utilize glucose.

Thin Metabolic Syndrome or Cushing’s Syndrome Horse--The diet for this type of horse is basically the same as the previous with the addition of extra calories in the form of fat and/or concentrate with a low non-structural carbohydrate level (low starch and sugar). Beet pulp is an excellent feed ingredient for these horses because it is low in NSCs but higher in calories than hay alone; it does need to soak in water before feeding, however. Beet pulp also works well for horses with dental problems. Fat can be fed in the form of rice bran or canola oil.

There are also several commercial diets now available for horses sensitive to starch and sugar. Most feed companies have developed their own versions, such as Nutrena’s Safe Choice™ and Lite Balance™, LMF’s Low NSC Stage 1™ and Complete™, Purina’s Well Solve™, and Elanbaas’ Nutracool ™and Equibalance™. Talk to your equine nutritionist or veterinarian for help deciding which may be the best choice for your horse’s specific needs.

What about grass? In general, lush green fast-growing grass is a problem for these horses. For much of the country, this growth happens in springtime. In northwest Washington, grass can be a problem through spring, summer, and the beginning of fall. Dr. Nicholas Frank offered a great guideline at this year’s American Association of Equine Practitioners conference: “Clients [should] pay attention to their lawn when managing an affected horse (horses prone to founder easy); their animal should be held off pasture when the lawn needs more frequent mowing.”

Grazing muzzles are a lifesaver for the overweight or sugar-sensitive horse. They allow the horse to be on pasture and get the exercise and nutrition they need while avoiding rapid weight gain and usually preventing laminitis.

As with any nutritional or medical issue with your horse, talk to your veterinarian before any management or feed change. Not every diet works the same for every horse. Also, horses with metabolic problems often have various other medical issues that need to be addressed, such as immunity problems, dental issues, and musculoskeletal concerns. Your vet can help you keep your horse at his best for many seasons to come.