Equine Cushing's Disease- The Basics

You may know of an older gelding at the barn that looks kind of shaggy and has weird fat deposits on his body. You often forget to ask his owner about it – or you may be too embarrassed to ask in the first place. What’s going on with that horse? Could it be Cushing’s disease?  

It is good for every horse owner to know the basics about Cushing’s disease. More horses are becoming ‘pets’ long after they have retired from work and age-related diseases are on the rise. Cushing’s is considered a disease of older horses, as it happens mainly in horses over 18 years of age. But sometimes ‘youngsters’ can suffer – as young as 5 years of age. Let’s take a closer look at Cushing’s disease and how nutrition may play a role in keeping it at bay.

What is Cushing’s Disease?
Cushing’s disease is also known as hyperadrenocorticism. It can also happen in dogs and humans, but the disease process is markedly different. Cushing’s happens when the pituitary gland in the horse’s brain ‘miscommunicates’ with the adrenal glands. In return, the adrenal glands produce too much of a hormone called cortisol. You may have heard of cortisol as a “stress hormone.” In horses, this disease is better known as “pituitary pars intermedia dysfunction.” 

Excess cortisol can cause a variety of problems in the body. Most of them we can easily identify in horses. Signs may include:

• Shaggy hair coat
• Incomplete shedding
• Delayed shedding
• Deposits of fat along the neck, topline and tail head
• Excess thirst
• Excess urination
• Chronic laminitis
• Obese body condition 
• What does diet have to do with it?

Cushing’s disease in horses is not fully understood, damage to neurons in the brain can precipitate into a problem with the pituitary gland. According to Dr. Philip Johnson at the Western Veterinary Conference in 2012, “oxidative stress-mediated degeneration of dopaminergic neurons in the periventricular aspects of the hypothalamus appears to play a central role.”

So what does that mean in plain English?  This means that oxidative stress is part of the reason that Cushing’s disease develops in some horses. Oxidative stress is caused by reactive oxygen and free radicals in the body. These “bandits” are created by a variety of things – from normal metabolism to stress and pollution. They in turn can damage cell membranes and DNA – leading to cell death. The body has a variety of ways that it can “cope” with free radicals. However, genetic mutations, certain disease states, stress, age and other factors can inhibit this – allowing for oxidative damage to take its toll. 

While oxidative stress and how it damages the body is a very complex subject, the body uses a few things to combat it. Antioxidants from the diet are used in its fight against oxidative damage as well as certain antioxidant enzymes. If there aren’t enough in the body – oxidative damage can occur at a faster rate. 

Could we prevent this oxidative damage that causes Cushing’s disease in horses?  It is hard to say, and there is no scientific evidence yet that you can. However, improving your young or older horse’s diet by including antioxidant-rich foodstuffs, like flax and sea buckthorn berry may certainly help tip the scale in your horses’ favor. 

Sea buckthorn contains a variety of bioactive antioxidants and minerals such as zinc and magnesium, which may be helpful in supporting animals with Cushing’s disease.
If you notice any of the aforementioned signs, talk to your veterinarian. Another condition, called Equine Metabolic Syndrome (Peripheral Cushing’s Syndrome) can also cause similar signs. 
If your horse already suffers from Cushing’s or Equine Metabolic Syndrome, talk to your vet about using high-antioxidant foodstuffs as an adjunctive treatment or nutritional support.

Resources
(1)Huey-Chun Huang, et al., Inhibition of melanogenesis versus antioxidant properties of essential oil extracted from leaves of Vitex negundo Linn and chemical composition analysis by GC-MS Molecules. January 2012;17(4):3902-16.
(2)McFarlane, D.  The Role of Oxidative Stress and Neurodegeneration in Equine Pituitary Pars Intermedia Dysfunction: A New Look at an Old (Horse) Disease. ACVIM Forum Proceedings. 2005.
(3)Johnson, P. Equine Cushing's Disease (Pituitary Pars Intermedia Dysfunction): Pathophysiology & Clinical Recognition (EQ9). Western Veterinary Conference Proceedings. 2012.
(4)Messer, N. Endocrine Disorders of the Horse. Western Veterinary Conference Proceedings. 2010. 

Always consult with your veterinarian before starting a new medication, remedy or nutritional supplement. The information provided in this article is for educational purposes only – it is not intended to diagnose, treat or cure any disease process.