Cushing’s Disease in Horses


Why is Cushing’s disease diagnosed so frequently in horses these days? This disease has actually been in the equine population for many years, but generally went unrecognized. There have always been many unexplained cases of laminitis occurring in the winter or early spring when there is little grass, and we have often seen older horses with inexplicably long hair. Cushing’s only seems to be increasing because of a better understanding of the diagnostic tests involved.

Laminitis is one of the more frustrating complications of Cushing’s disease. Chronic cases can take a lot of time and energy to treat and still not respond satisfactorily. Natural medicine provides another toolbox of treatments to help both acute and chronic cases. The goal in natural treatment of Cushing’s disease and Cushing’s-based laminitis is to:

• Provide nutritional support to prevent and reverse damage from circulating free radicals

• Prevent further damage to and encourage healthy laminar attachments

• Return the horse’s metabolism to proper balance.

When managed correctly, with patience and attention to detail, most chronic cases can return to reasonable work. Poorly responsive cases can often be managed and kept relatively comfortable without the use of drugs.

What is Cushing’s disease?
It has been thought that horses, as part of the aging process, get pituitary adenomas (tumors) of the pars intermedia part of the pituitary gland. But texts disagree about how common the true adenoma tumor is. About half the sources feel the actual adenoma is less common and that there is a hyperplasia instead (abnormal and overactive, but not tumor growth, of the cells). Both adenomas and hyperplasia cause similar sets of symptoms. The hyperplasia, however, being a functional disturbance rather than a tumor, may be easier to treat. Many horses respond well to treatment; these cases are probably more functional than cancerous. Horses that do not respond well to treatment may have an actual tumor.

Why Cushing’s disease occurs is not understood. One theory is that chronic stress (from the horse’s younger life) could lead to the development of hyperplasia and then perhaps progress into a tumor. There are no clear answers at this point.

Laminitis that occurs for no outward reason is one of the most serious symptoms of Cushing’s disease. Some of the most refractory cases of Cushing’s-based laminitis occur in the winter, an uncommon season for typical cases. Even the more common summer laminitis, which appears to be caused by overeating grass, can be quite difficult to treat, especially when other clinical signs of Cushing’s are present.

Many horses diagnosed with Cushing’s laminitis are overweight and very easy keepers, sometimes unable to eat more than a small amount of hay each day to control their weight. They generally have cresty necks and fat pads in specific places. The fat pads are typically behind the shoulder blades, on each side of the tail, and along the lumbar area. The fat on the body is often visibly lumpy. In some cases, horses who were previously easy keepers suddenly start requiring more food to maintain body weight. They may maintain their fat pads despite the obvious weight loss.

Diagnostic tools
• The most important diagnostic tool for identifying Cushing’s disease is the horse’s history and the clinical signs discussed above. A thorough physical exam may reveal some of the less obvious signs such as poor teeth and reproductive problems.

• Supporting lab work can be helpful and should be performed if possible, but may be inconclusive. Part of the problem is that in equine practice, single blood samples are taken whenever the practitioner is at the farm, so there is little standardization in the timing of the samples. Many of the parameters have daily variations and may change due to stress or other factors, including the amount of exercise a horse has had before the blood was drawn.

• Cortisol levels appear to be an inaccurate test for Cushing’s disease. Elevated blood cortisol can indicate high levels of stress in the body – but is the high cortisol coming from the Cushing’s, or has the Cushing’s come from the chronic stress caused by something like laminitis? High levels of cortisol suppress the immune system and contribute to more infections in these horses. Cortisol is the stress hormone, so both past and present stress are contributors.

• Resting insulin levels, ACTH, and glucose tests are sometimes used. The usual single-sample thyroid test does not give a true picture of thyroid function because there is significant variation in thyroid levels even in normal horses.

• The low dose dexamethasone suppression test (LDDS) is perhaps the most frequently used, but I would avoid it since dexamethasone is a steroid, and sensitive horses can get laminitis from steroids. I have seen a number of serious cases of laminitis in Cushing’s horses after steroid injections.

• Some new laboratory profiles are being offered that combine tests taken at various times of the day. These may be more accurate in positively diagnosing Cushing’s disease, although the tests often add little extra information to the clinical signs and basic blood tests.

• Also, have your veterinarian collect a complete blood count (CBC) to examine immune system status, and a chemistry screen to check organ function.

Insulin resistance
Cushing’s disease in horses has many of the same characteristics as insulin resistance. Many Cushing’s horses have elevated insulin levels in their blood. Normally, when a sugar or carbohydrate is eaten, blood sugar levels increase, insulin is secreted by the pancreas, glucose is carried into the cells by the insulin and the blood sugar goes back to normal. In insulin resistance, the cell walls are too stiff to let the insulin do its job properly. The glucose gets stored as fat instead of providing energy for the cells. Many horses store their fat in specific places, such as fat pads on their body and in the crests of their necks.

Holistic treatment
Many tools in the alternative medicine toolbox can treat the Cushing’s horse, but each animal is an individual and will respond differently. In treating these complex cases, it is important to take it one step at a time and realize that the course of treatment may be long and expensive if the horse has many medical problems. There isn’t one simple answer. I try to look at how severe and longstanding the clinical signs are to determine how much to do at one time.

In many cases, homeopathy is important to the treatment’s success, but it is advisable to work with an experienced homeopath. Chinese medicine, both with acupuncture and herbs, can also be used to help Cushing’s horses. Again, it is best to work with a veterinarian experienced in these modalities.

Good nutrition is crucial
Nutrition plays a key role in the holistic management of Cushing’s horses.

1. Many horses have been given anti-inflammatories and antibiotics frequently throughout their lives. This compromises the health of the digestive tract in many ways. So the most important thing to do is restore the gut function with high quality probiotics. If the gut is in poor shape, 20 grams of glutamine (an amino acid that acts as a fuel for cells of the gut wall) per day will help.

2. Feed whole foods if possible, unless the horse has poor teeth or digestion. Processed grains and hays may lose key ingredients during manufacturing since pellets and extruded feeds are made at high temperatures. Some horses digest their food better when digestive enzymes are added.

3. The feed should be low in sugar! There is no need for any sweet feed. Plain whole grains are effective, or if you need to purchase a processed grain, get a low carb feed. Plain corn (about 25%), barley (about 35%), and oats (about 45%) make a simple, clean mixture, and any combination of these grains can be used based on their availability in your part of the country. From a Chinese medicine perspective, barley is a cooling food and is useful for inflammation.

4. Higher levels of protein (up to 14%) and calories may be needed in horses with weight loss problems. Increased calories can be given as fats (vegetable oils or rice bran), and are well digested by most horses. Animal fats should not be used due to the preservatives used in the processing and the fact that horses are vegetarians.

5. High levels of antioxidants are needed. Coenzyme Q10 is very valuable in this respect. The therapeutic dose is 300 to 600 milligrams per day for the first week or two, after which the amount can be decreased slowly to a maintenance dose of about 100 milligrams per day. Vitamin C is an excellent antioxidant and nutrient for collagen support as well as organ and immune system healing. Doses range from 3 to 8 grams per day.

6. One of the most important aspects of any nutritional program for horses is free choice minerals, with salt fed separately. Several key minerals are needed for glucose metabolism. Magnesium affects insulin secretion and its action in the cells. It also helps the cells become more flexible and permeable to insulin. Chromium helps make muscle more sensitive to insulin so glucose can be taken into the muscle cells more easily. Chromium has also been shown to be effective in reducing fasting blood sugar levels. Vanadium, or vandyl sulfate, has actual insulin-like effects on glucose metabolism and helps transport glucose into the cells.

7. Essential fatty acids (EFAs) help make cell walls more permeable to insulin – they are also anti-inflammatory and improve the health of the immune system. Omega 3 fatty acids are especially deficient in many equine diets. Most high fat equine foods use highly saturated animal fats that are full of preservatives. Flax and hemp oil provide plenty of Omega 3 fatty acids that are palatable to the equine.

8. I often use pituitary glandular support along with general glandular support, because the pituitary gland is central to the function of the entire hormonal system. Glandulars are nutritional supplements made from actual glandular tissue, often prepared with supporting nutrients. In small animal and human medicine, they are commonly and successfully used both as replacement therapy for poorly functioning organs and when there is evidence of inflammatory or degenerative processes in the organs.

Glandulars can be useful in equine nutrition and should be considered instead of synthetic organ replacement, as in thyroid therapy or support for other organs such as the pituitary gland. Cushing’s horses are about the only ones I will use glandulars for because of the vegetarian nature of the horse. Additional thyroid supplementation may be necessary in some cases.

Treat each horse as an individual and seek quality practitioners to help you. Use as much whole food nutrition as possible, supplement with specific nutrients as needed, reduce stresses and vaccinations, and support a healthy digestive tract. Over time, you will learn to manage your horse’s Cushing’s disease effectively, maintaining a healthy, happy medium with your equine partner.


Joyce Harman, DVM, MRCVS, graduated in 1984 from Virginia Maryland Regional College of Veterinary Medicine. She is certified in veterinary acupuncture and chiropractic and has completed advanced training in homeopathy and herbal medicine. Her practice in Virginia uses 100% holistic medicine to treat all types of horses. Her publications include The Horse’s Pain-Free Back and Saddle-Fit Book – the most complete source of information about English saddles – and The Western Saddle Book is on its way. www.harmanyequine.com.

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