Equine Metabolic Syndrome
R. Paul Schwab, D.V.M.
Kulshan Veterinary Hospital
Spring is here and so are the lush green pastures, which for many horses can be a great source of nutrition and for others a source of pain and frustration. Some breeds and individual horses can be quite sensitive to the high sugar content of new spring grass, putting on weight dramatically and foundering easily. Certain individual horses and ponies will even founder on what seems like a bare pasture. This article will be addressing such animals and what may be going on metabolically in their system.
Equine metabolic syndrome is a recently developed term describing horses that are insulin resistant, obese, and tend to deposit fat in places such as the crest of the neck, the sheath, and on the rump near the tail head. These animals tend to gain weight very easily (“easy keepers”) and are more likely to founder.
Obesity can be a common problem in backyard horse farms due to overfeeding and lack of exercise especially in older horses that may have lameness issues already. In addition some breeds are genetically programmed to be able to gain weight easily during periods of forage availability for preparation for times when food is scarce. Now forage and good feed sources are available throughout the year. Also, many horses are confined to small paddocks or stalls and may get little or no exercise.
The fat that these horses deposit in their body has actually been found to be hormone producing similar to glands like the adrenal and thyroid. These hormones are thought to cause insulin resistance which prohibits the body from utilizing and metabolizing glucose normally. Insulin normally is secreted by cells in the pancreas in response to glucose in the body after a meal. Insulin stimulates uptake of glucose by the liver, muscle, and fat. It also decreases production of glucose by the liver. In animals that are insulin resistant, the insulin doesn’t work at the cellular level, resulting in excess free glucose in the blood and its distribution to cells that don’t need it. Other causes of insulin resistance in addition to obesity are stress, genetics, glucocorticoid administration (steroids), and diet, especially high starch diets and high sugar grasses.
Long-term elevated blood glucose can be detrimental on the health of the horse. The pancreatic cells that produce insulin may become exhausted producing a situation similar to diabetes in people. These horses tend to have more problems with tying-up and increased muscle damage during heavy exercise as well as early arthritis because of cartilage damage. There is some thought that this syndrome may be a precursor to Equine Cushing’s Syndrome.
Of primary interest this time of year is laminitis (“founder”). The high glucose levels can be toxic to the endothelial cells that line blood vessels. Because of the complex nature of the blood vessels in the feet they tend to be very sensitive to damage and inflammation. This inflammation activates enzymes that cause separation of the hoof wall from the coffin bone and result in pain and possible rotation of the coffin bone that accompanies clinical laminitis.
Horses that have Metabolic Syndrome tend to be between the ages of 8 and 20, are “easy keepers,” have abnormal fat deposition, and founder easily. Breeds that seem to be over represented include Morgans, Ponies, Mustangs, Donkeys, and Paso Finos. Diagnosis may be made on the basis of clinical signs, history, or by laboratory methods. They tend to have high blood insulin levels and may have low thyroid hormone levels.
Management consists of exercise and nutrition. Strict weight control is imperative. Exercise will not only encourage weight loss, but will also help the horse utilize the glucose better.
When feeding these horses, starch and sugar must be avoided. Avoid starchy high glycemic index feeds such as corn, oats, barley, and molasses. Reduce the amount and time they spend on lush new grass. New grass contains high fructans that are the sugars that cause laminitis [Note: Grazing muzzles are an excellent way to slow down grass intake and allow the horse to be out in the field without foundering]. Feeds that are OK to feed include most grass hays, beet pulp, soy hulls, and if needed to keep weight on, rice bran or vegetable oils (canola or corn). If your hay is particularly exceptional, you may want to soak it to reduce the sugar content.
Other supplements that might be helpful include Vitamin E and Selenium to help prevent damage to the endothelial cells and Chromium that may help with the insulin resistance. Thyroid hormone supplementation may be of use in some horses.
