The hypothyroid laminitis horses are almost always overweight. They are easy keepers and will have aggravations in their symptoms if they get even small amounts of grain or fresh green grass. Their fat is fairly evenly distributed over the body with p
ons over the withers and tail head. They can have dull hair coats or other hypothyroid symptoms, but often appear overall to be healthy, happy, well-adjusted horses with the exception of their laminitis. Some horses show signs suggestive of decreased thyroid function yet have normal levels of circulating thyroid hormones.
Laminitis in the hypothyroid horse is usually associated with overeating or excessive weight causing mechanical damage. Vaccinations tend to aggravate or precipitate laminitis episodes. Hoof abscesses are very common and can be recurrent. Overall hoof wall quality is often good but can deteriorate with long-term poor digestion. There is the tendency to develop thrush.
Hypothyroid type horses tend to be prone to fluid imbalances and do not do as well in humid climates. They tend to have trouble with assimilating nutrients so providing nutrient-dense food source vitamins and minerals is important. For this reason, a small amount of alfalfa hay can be fed along with grass hay. Because of the tendency to overeat and get obese, pasture often needs to be limited at least until the horse has recovered enough from the laminitis to go back into work.
I have not found Magnesium supplementation to be of as much value in these horses as the insulin resistant types (see below). While the hypothyroid horses can have large cresty necks, this usually accompanies overall obesity and the crests will get smaller as they lose weight. The hypothyroid types generally do not have the tight hard muscles and crests seen with insulin resistance. If Mg is deficient in the diet, the hypothyroid horses can benefit from it being supplemented and you may see improvement in symptoms such as muscle soreness after work.
Pituitary -- Cushing's disease
Laminitis in these horses is secondary to a tumor of the pituitary gland. The pituitary gland is considered the master gland in the body and controls the release of many hormones including ACTH. ACTH stimulates the release of natural steroids by the adrenal glands and this process would normally be regulated by an inhibitory dopamine feedback system. Cancerous cells in the pituitary do not respond to this feedback system so the steroid levels remain elevated, creating serious consequences. These horses are generally aged and, in addition to laminitis, have other symptoms such as excessive drinking, poor shedding, weight loss, poor wound healing and muscle wasting. These tumors are common in old horses. Unfortunately, there is not a cure for this condition; however, supportive nutrition and minimizing stress can allow these horses to live a quality life for some time.
Insulin resistant laminitis
Many horses have elevated blood insulin levels, without concurrently raised or lowered glucose levels. A relatively new condition is being recognized in human medicine, currently called syndrome X or insulin resistance syndrome. Syndrome X is a group of symptoms related to insulin resistance or hyperinsulinemia. It is characterized by an inability to transport glucose into cells. Cushing's syndrome in horses has some of the same characteristics as syndrome X.
People who are susceptible to syndrome X are frequently from a genetic type considered "thrifty" or in horse terms, "easy keepers." In this type of individual, horse or human, the body is very efficient at storing fat for times of need, and in fact, if fed less, they often become more efficient at storing fat. In humans much of the fat stored from impaired glucose metabolism is distributed centrally, especially around the abdomen. Many horses store their fat in specific places including fat pads on their bodies and cresty necks. The symptoms of insulin resistance are very similar to equine Cushing's disease. One important difference is the age of affected horses. Insulin resistance often occurs in middle-aged horses. The nutritional support used for insulin resistance is the same as that used when treating Cushing's horses. The permeability of the cell walls to insulin is enhanced and nutrients are provided to help insulin and glucose pathways function better. The good news is many of these horses respond to treatment and can recover if managed well and given enough time.
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Madalyn Ward, DVM, publishes the monthly newsletter, "Holistic Horsekeeping," and is the owner of Bear Creek Veterinary Clinic in Austin, TX. She is certified in Veterinary Homeopathy, Chiropractic and Acupuncture, and is a member of the American Veterinary Medical Association, American Association of Equine Practitioners, American Holistic Veterinary Medical Association, Academy of Veterinary Homeopathy, and the International Veterinary Acupuncture Society. Contact her at 512-288-0428, or visit www.holistichorsekeeping.com .