Two common health conditions that affect older horses are equine metabolic syndrome (EMS) and equine Cushing’s disease. While there is some overlap in their clinical presentations, it is important to outline the differences so that you can know your options for diagnostics and treatments in your horse.
Equine metabolic syndrome
EMS is characterized by obesity (or a lean body condition with fat pad development) and insulin resistance. Some think of it as similar in pathology to Type II diabetes.
Pony breeds, Morgans and Paso Finos are just a few of the breeds that are more commonly affected by this condition.
Many horses with metabolic syndrome develop fat deposits, classically in the neck (cresty neck) and tailhead regions. Often owners will report difficulty getting their horse to lose weight, even on a restricted diet. In mares, a common complaint is infertility
Typically, the most concerning consequence of a horse developing EMS is an increased risk of laminitis. Horses with EMS frequently suffer from chronic laminitis and associated abnormal hoof growth rings. These are painful conditions and can be career — and even life — threatening.
Diagnosis of EMS
So how do we arrive at a diagnosis? The process is not always straightforward, but it generally involves a thorough history and a physical exam. In addition, blood work can help us determine if your horse is demonstrating hyperinsulemia (too much insulin compared to carbohydrate intake).
Hyperinsulinemia is a major risk factor for laminitis, and subclinical laminar damage can progress over years before diagnosis. Therefore, early recognition and management of EMS — prior to the onset of laminitis — is the goal
Treatment of EMS
Treatment of EMS can vary significantly among horses, but most patients respond to changes in management, including restricting grass intake, increasing exercise and feed changes. For horses needing a bit of extra support, drugs such as thyroid supplementation and some newer therapies are available.
Insulin resistance, seen with EMS, is worsened by corticosteroids. The use of certain drugs such as dexamethasone powder or prednisone should be reevaluated in patients with EMS. This connection to corticosteroids is why equine Cushing’s disease is often associated with EMS, as Cushing’s disease causes increased “natural” corticosteroids in the horse.
Equine Cushing’s Disease
Equine Cushing’s disease (which is slightly different than the Cushing’s that affects humans or dogs, for example) primarily affects horses over the age of 15.
When people think of Cushing’s disease, they often picture a horse with a long curly hair coat and a pot-belly.
But it’s important to know that we see many horses with Cushing’s disease who never develop this appearance.
Cushing’s disease is characterized by a benign tumour of the pituitary gland (pituitary adenoma), which results in an increased secretion of various hormones and eventually leads to an increase in blood cortisol levels.
Cortisol, a steroid, is an important hormone for things like the inflammatory response, the regulation of muscle tone and connective tissue, and balancing insulin levels. Changes to cortisol levels can cause a huge variety of clinical signs. Among the most common are:
- A higher susceptibility to various infections such as foot abscesses
- The pot-bellied appearance that results from the weakening of abdominal musculature
- Increased drinking and urination due to changes to blood flow at the level of the kidney
- Laminitis due to the changes on blood flow and insulin regulation (also seen with EMS, above)
Other clinical signs to watch for include:
- Hair coat changes
- Increases in appetite
- Excessive sweating
- Blindness
Diagnosis and treatment of Cushing’s disease
Cushing’s is diagnosed through various blood tests. There are no treatments available to remove the tumour and the disease is not curable, but it can be managed with daily medications, commonly pergolide.
Therapies focus on antagonizing the hormonal changes associated with the disease. If treatments are started early in the course of the disease, horses can lead happy, normal lives. However, if a horse is diagnosed after a significant episode of founder, the medications may not reverse the resulting damage.
For this reason, we generally recommend screening older horses (age 15 and up) for Cushing’s disease during their annual exams.
Disease overlap
From time to time, both EMS and Cushing’s can occur in the same patient. Some horses with EMS will later develop Cushing’s.
Due to the similarities between the diseases, we advise that horses with regional adiposity and laminitis should be tested for both EMS and Cushing’s, especially horses over 15 years of age with the clinical signs described above.
