Equine Cushing’s Disease and Equine Metabolic Syndrome
Equine Cushing’s Disease or Pituitary Pars Intermedia Dysfunction (PPID) is one of the most common hormonal disorders in horses and ponies. Any horse or pony can be affected by Cushing’s disease and while it is generally assumed that this is only a problem in geriatric patients, in fact, any individual over 10 years of age can develop Equine Cushing’s disease.
The disease arises when the nerves supplying part of the pituitary gland, situated at the base of the brain, degenerate and produce insufficient levels of the hormone dopamine. Dopamine is important in regulating production of cortisol and this results in the majority of clinical signs we see with the disease. By far the most common and concerning clinical sign associated with Cushing’s disease is laminitis or founder. For many years, researchers believed that laminitis was directly linked to the sugar levels in the grass however there is now a lot of evidence to suggest that whilst is does play a role in causing laminitis, up to 90% of horses and ponies with recurrent laminitis are affected by Cushing’s disease or Equine Metabolic Syndrome (see later). This explains the observations that some horses develop laminitis and others grazing the same pasture do not. Other common clinical signs of the disease are:
- Abnormal coat length or shedding: this can be very mild or absent in the early stages
- Abnormal fat deposits particularly in the hollows above the eyes
- Excessive sweating
- Increased appetite and thirst
- Increased urination
- Recurrent infections
- Delayed wound healing
- Loss of muscle condition – ie a pot belly appearance
A number of different blood tests are available to assist the diagnosis of Equine Cushing’s Disease. The easiest and most common is a single blood test that measures levels of the hormone ACTH. Although there is no cure as such, there is a good treatment option available for this disease. The drug is called Pergolide and is available currently in liquid form but soon to be available in dissolvable tablet form. Pergolide acts directly on dopamine production and helps to normalise hormone production from the pituitary gland. It can take up to 6 months to see the full benefits of treatment but it is often reported that there is an improvement in demeanour within a few weeks of starting treatment.
Above shows the resolution of clinical signs from day 1 through to approximately 6 months after commencing pergolide treatment.
There are a lot of other remedies and supplements that claim to be successful in treating Equine Cushing’s Disease but so far only one treatment (Pergolide) has demonstrated sufficient treatment benefits and safety to become a licensed treatment. Whilst medication is essential in controlling the clinical signs and reducing the risk of laminitis and infections, it is also important to consider other management aspects. Affected horses and ponies also benefit from regular worming, dental care, foot care and dietary management.
Equine Metabolic Syndrome
Equine Metabolic Syndrome or EMS is another hormonal disease of horses and can be likened to Type II diabetes in humans. Whilst the disease process is different to Equine Cushing’s there are many similarities between the two and they often occur simultaneously. The main characteristic of EMS is insulin resistance. Those affected are often overweight or have abnormal fat distribution (ie they can look underweight but have abnormal fat deposits around the eyes, shoulders and tail) have difficulty losing weight and have a history of recurrent laminitis. Diagnosis of EMS is usually based on demonstrating high levels of insulin and triglycerides (fats) in a resting fasted blood sample. This involves taking a blood sample after an overnight fast ie with a muzzle or keeping stabled overnight. The definitive test is an in feed glucose challenge test where insulin levels are tested after a prescribed amount of glucose is given orally after a period of fasting.
The main stay of treatment for EMS is diet and exercise, just as is the case for type II diabetics. This involves implementing a well balanced high fibre low carbohydrate diet with regular exercise. The drug Metformin is used in human medicine as an oral hypoglycaemic ie it lowers blood sugar levels. Its use in horses is a little controversial amongst researchers however clinically it certainly seems to yield good results in the initial stages of management.