Meddleton Equine Hospital

Equine Cushing's disease is usually caused by a Pituitary Adenoma, or Pars Intermedia Dysfunction; a benign tumor of the pituitary gland. It generally occurs in horses greater than 15 years old. Common signs include hirsutism (excessively long hair coat) that does not shed out in the spring, excessive sweating, increased water consumption with increased urination, (normally horses will consume 5-7 gallons of water daily), loss of muscle tone or mass, especially over the back or croup, and may appear pot-bellied@ or sway-backed. Horses may lose condition despite a normal or increased appetite. Due to increased systemic levels of cortisol, horses are more susceptible to infections, ulcers, sole abscesses, and laminitis (founder). The classic picture is one of an old foundered pony with a long, thick hair coat well into the summer.

Because the pituitary is the Master Gland controlling all of the other endocrine glands in the body, there are a myriad of possible complications associated with a pituitary adenoma. Affected horses often low blood thyroid levels and increased blood ACTH, cortisol, insulin, glucose, and triglycerides.

A dexamethasone suppression test can be done to diagnose pituitary adenoma. In this test a small dose of dexamethasone is given and blood samples are collected in the late afternoon and the following morning. The disadvantages of this test are the expense and the risk of causing the horse to develop laminitis.  Another method is a screening test to determine blood levels of insulin, ACTH, triglycerides, cortisol, thyroid hormone, and glucose.

The most effective treatment for equine cushing's is pergolide. The effectiveness of the treatment can be determined by monitoring blood insulin and ACTH. These can be used to adjust the dosage to obtain the lowest appropriate dose. Initially I recommend testing every 3-4 months. Once stabilized, you can test on a yearly basis.  Vitamin E supplementation at a level of 9,000 IU per day is also recommended.

There are specific dietary considerations that should be observed. Sweet feed, molasses, grain (oats, barley, and corn, etc), wheat bran, beet pulp, and alfalfa should be minimized or eliminated. Feed grass hay, or a mixed hay with no more than 25% of alfalfa at a rate of 1.5% to 2% of body weight.

Equine Metabolic Disease

Is your horse young, overweight, laminitic, and getting almost nothing to eat?

This is another form of equine cushing's disease that has recently been recognized. It is also called Insulin Resistance, Omental or Peripheral Cushing's Disease or Obesity-Associated Laminitis Syndrome. These horses are overweight, have difficulty losing weight, and have the fat distribution typically associated with hypothyroidism (cresty neck, slab-sided, fat rolls at the tail-head). Geldings often have a swollen sheath, mares are often infertile, and all are prone to laminitis (founder). They do not have the long hair coat and the increased drinking and urination. These horses are often young compared to the typical pituitary adenoma horse.

Testing for Equine Metabolic Disease is similar to classic Cushing's Disease, but the dexamethasone suppression test is normal. Blood levels of insulin, glucose, and triglycerides are elevated. Thyroid hormone may be normal, or may be low as a secondary aspect of the disease.

Treatment for Equine Metabolic Disease is Chromium supplementation for life. Magnesium supplementation is also advised. Both of these minerals help to control the horse’s natural insulin resistance. Dietary restrictions as advised above should also be observed.