McKee-Pownall Equine Services | Health Care FAQ

Health Care FAQ

Lions, and Tigers, and .... Equine Cushing's Disease? Oh My!!!

We all have seen the big crested necked horse with the long shaggy hair coat out in the field and couldn't help ourselves from taking a picture of the eccentric looking fellow. But have you ever wondered what the underlying cause is or if it is normal? Unfortunately many of these horses suffer from a condition called Equine Cushing's Disease.

What in the world is Equine Cushing's Disease?

Equine Cushings Disease is a condition that results from hormonal imbalances created secondary to enlargement of the pituitary gland. The pituitary gland is located at the base of the brain and as it enlarges it compresses adjacent structures leading to their loss of function. For those academic buffs out there here's a little fun fact - due to the primary source of the disease the condition is better referred to as Equine Pituitary Pars Intermedia Dysfunction (PPID). Majority of cases are seen in our elder patients (85% over 15 years of age) but has been seen in horses as young as 7 years old. Increased incidence is seen amount ponies and Morgans but any breed can be affected. 

Now that the condition is on your radar what should you be looking for?

Sometimes identifying these suspects can be as easy as pointing to the woolly mammoth in your pasture. This long wavy haircoat that fails to shed normally is referred to as  hirsuitism. Unfortunately, as the veterinarian, we sometimes are not called to see these patients until they have acutely developed laminitis. Early symptoms owners can identify is excessive drinking and urination, abnormal fat desposits (supraorbital fat, cresty neck, fat around tail head), lethargy, excessive sweating, muscle mass loss, infertility. Another common symptoms in these horses is repeated infections such as sole abscesses, tooth root infections, and sinusitis

Once we have a suspect what steps do we take to confirm our suspicions?

Advanced cases may be diagnosed on clinical signs alone. In cases where symptoms are mild there are blood tests that are used, unfortunately no tests is 100% accurate.

Dexamethasone Suppression Test requires 2 blood samples and is an overnight protocol. An initial blood sample is taken, then a low dose of dexamethasone is administered. The next day a second blood sample is taken and the cortisol levels are compared. Normal horses will have a lower cortisol level in the second sample due to negative feedback from the dexamethasone injection. In horses with Cushing's Disease no suppression (or a minimal amount) will be seen in the second cortisol measurement. There are drawbacks to this test – it requires two farms visits and the risk of laminitis is increased in horses suffering from Cushing's Disease from the dexamethasone administration.

Measurement of resting ACTH levels is another blood test that is preferred by veterinarians. Horses with Cushings Disease will have pituitary glands that produce significantly higher levels of ACTH. Stress and pain can produce false positives and results may vary in the fall.

Horses may be insulin resistant as well, so blood tests evaluating insulin and glucose levels may be important in determining treatment and diet options. 

Is there hope for horses suffering from Equine Cushing's Disease?

There are many options for management of these horses. It is very important to realize the goals of treatment is to improve quality of life and reduce clinical signs; unfortunately complete resolution of the disease is unlikely and management is lifelong.

All cases require supportive care such as regular dental and hoof care, deworming, clipping of hair. Medication will be required as symptoms progress. Pergolide is the treatment of choice – the dose may vary on a case by case basis or depending on the season.

Diet is very important in these cases where insulin resistance may be contributing to clinical symptoms. Avoid diets high in soluble carbohydrates and feed diets high in fibre and fat. Soaking hay for 30min with cold water can help lower the sugar content. A grazing muzzle is highly recommended for these patients. Please consult with your veterinarian for the best time to allow your horse to grass as the sugar content in grass fluctuates depending on temperature and climate.

There are countless adjunctive therapies available and consulting your veterinarian is highly recommended to determine the best course of action for your horse. Exercise is recommended to help with fat metabolism and promote insulin sensitivity. A balanced vitamin/mineral supplement high in B vitamin. chromium and magnesium is beneficial in most cases.

The key in any case is early detection and developing a treatment plan with your veterinarian to diagnose, treat and closely monitor your horse.