Studies have shown that approximately 15 to 30 percent of horses and ponies more than 20 years old suffer from equine Cushing's disease. The condition is also known as pituitary pars intermedia dysfunction (PPID), and it affects both males and females of every breed. PPID is characterized by an enlargement of the horse's pituitary glands, those parts of the endocrine system responsible for the production and regulation of hormones. These hormones are what control the horse's various bodily functions (from hair growth to weight management), meaning that those horses that suffer from a hormone imbalance will exhibit irregular patterns of each.
A slow disease
PPID progresses extremely slowly as a horse ages. As such, it is often easy to miss the early warning signs of the disease. However, once PPID has progressed into its advanced stages, it is fairly easily diagnosed based on a number of clearly visible symptoms. These include a patchy coat, weight gain in unusual places (such as around the eyes) and muscle wasting. A horse that is suffering from late-stage PPID will often be quite lethargic and is at risk of developing laminitis.
If detected early, PPID is somewhat manageable. However, it remains difficult to identify the subtle symptoms of early-stage PPID. There are two types of tests that a veterinarian can use to diagnose horses with this condition. The first is a dynamic test that will measure the responsiveness of the endocrine system to different stressors over time. The second type of test is a single assessment that screens the horse for various hormone levels. While both of these types of tests can give a vet a more complete picture of a horse's endocrine health, neither is a 100 percent accurate indicator of PPID.
Managing PPID through diet control
One of the best things you can do to help your horse weather the storm of PPID is to alter its diet to counteract the disease's effect. The key is to reduce the insulin levels in the horse's bloodstream. Much like humans, horses produce insulin in response to starch and sugar levels in the bloodstream. In order to reduce insulin levels, it is necessary to reduce the amount of sugar and starch in the animal's feed. Corn, oats and barley are all very high in starch and thus should be phased out of the horse's diet as much as possible if it is suffering from PPID.