Equine Cushing’s disease, scientifically referred to as pituitary pars intermedia dysfunction (PPID), is typically an age-related neurodegenerative disorder. Many horses will develop Cushing’s as they get older, but the symptoms come on so gradually, the disease often goes unrecognized. Usually around the age of 15 the risk becomes greater; however, younger and younger horses are developing PPID, which is a disturbing trend.
PPID is a progressive disorder, meaning it gets progressively worse over time. Cushing’s is not fatal in and of itself, but rather from the conditions it can lead to if left untreated, such as infections, muscle wasting, colic, and of course, laminitis. There is no cure, only treatment. However, by reducing oxidative stress, it is possible to slow down its progression.
This gland is suspended from the hypothalamus at the base of the brain. One of three lobes in the gland, the pars intermedia is responsible for equine Cushing’s disease; it produces adrenocorticotropic hormone (ACTH), the regulation of which is at the heart of the Cushing’s problem itself.
Elevated insulin, excess body fat, mental and physical stress, as well as environmental toxins can all lead to oxidative stress, resulting in the creation of a large number of proinflammatory molecules known as free radicals. These free radicals are volatile molecules that can destroy every kind of tissue. In the specific case of Cushing’s, progressively higher levels of oxidative stress damage the dopamine-releasing neurons until they can no longer function properly. Instead of producing dopamine (that would turn off the pituitary gland’s secretion of ACTH), dopamine secretion is diminished. Consequently ACTH secretion increases, telling the adrenal gland to produce more cortisol. And then the vicious cycle continues: Cortisol pulls glucose out of glycogen stores as well as breaks down muscle for amino acids (which also get converted to glucose). Elevated glucose stimulates the pancreas to release insulin. Insulin promotes body fat storage, which can lead to insulin resistance. Excess body fat releases inflammatory molecules, leading to free radical formation, damaging the dopamine-releasing neurons. Over time, this condition progressively worsens.
The diagram below illustrates this progression when body fat is regionally stored (indicating insulin resistance).
While most cases of PPID eventually require pharmaceutical treatment with pergolide, or its trademarked version, Prascend, other management approaches should always be implemented as a first line of defense. Reducing oxidative stress can slow down the destruction of dopamine-promoting neurons and therefore diminish the progression of Cushing’s disease. This can be accomplished by reducing inflammation-producing body fat (if the horse is overweight), modification of mental, physical, and environmental stressors, and feeding an anti-inflammatory diet.
Restricting forage is incredibly stressful.[i] And yet, this is the way many horse owners attempt to help their horses lose weight. The cascading negative effects of stress exacerbate this endocrine disorder in an already compromised horse into one with a higher risk for laminitis.[ii]
Don’t neglect exercise. It not only burns calories, but exercise makes cells more receptive to insulin, allowing the horse’s body to burn fat. The blood insulin level declines, thereby reducing inflammation and the risk of laminitis. Exercise also helps protect muscle mass (which the cushingoid horse is losing). Finally, it makes your horse more sensitive (less resistant) to leptin, a hormone that is supposed to tell your horse to stop eating.
You’re probably already paying close attention to the non-structural carbohydrates (NSC) in the diet. That’s important to help reduce insulin secretion. But, here are a few pointers to reduce inflammation:
PPID becomes progressively worse over time as dopamine-releasing neurons in the brain are damaged by oxidative stress. Through attention to damaging aspects of your horse’s lifestyle, diet, and environment, this neurodegenerative disease can be significantly slowed down.
[i] Getty, J.M. Restricting Forage is Incredibly Stressful.
[ii] Please read the article, "The Power of the Horse's Instincts" for more information, as well as Dr. Getty's books, "Equine Cushing's Disease - Nutritional Management" and "Easy Keeper," offering detailed, easy-to-do approaches to weight loss through free-choice forage feeding.
[iii] Antioxidants are offered in Dr. Getty's Free Shipping Store under the Anti-Inflammatory category.
[iv] Excellent sources of omega 3s are available in Dr. Getty's Free Shipping Store in the Omega 3 Supplements category.
For permission to reprint this article, in part or in its entirety, please contact Dr. Juliet Getty directly at Gettyequinenutrition@gmail.com.