Equine Metabolic Syndrome and Cushing's Syndrome


April 2008

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Equine Metabolic Syndrome

  2008 Cherry Hill   Copyright Information

Dear Cherry,

My 14 year old mare is an easy keeper, stays fat on grass and no grain and the last few years she has been shedding later in the summer. Could she have Cushing's syndrome?


Hi Tara,

I can not answer that question. Your veterinarian would be the one to ask. However, I suspect that your mare could have Equine Metabolic Syndrome. I'd like to give you some information to help you understand EMS and a few other similar conditions.

In the meantime, if when you say "grass" you mean grass pasture, you probably should remove your horse from pasture and feed her a regulated amount of grass hay instead.

Best of luck and please let me know what you found out when your veterinarian examined your horse.

Equine Metabolic Syndrome

Fat, overfed and under exercised, horses………are they just "easy keepers"? Maybe. But overweight horses are so much the norm these days that horses in fit condition run the risk of being called underfed, abused or starved. Just like humans, the US horse population is creeping toward obesity with all its attendant problems including a metabolic imbalance similar to type 2 Diabetes in humans. You don't want to let this happen to your horses, so take the time to read this article. It is one of those things that is best to know ahead of time to prevent !

Equine Metabolic Syndrome has also been called:

Peripeheral Cushing's syndrome (see Cushing's box below)
Pseudo-Cushing's syndrome
Insulin Resistance Syndrome
Central Obesity

What EMS is NOT:

Cushing's - Cushing's is an endocrine disorder causing pituitary disfunction - hormone imbalance and excessive cortisol production
Horses affected with Cushing's are usually between 18 and 23 years of age. Symptoms include:

  • hirsutism (long curly hair) with delayed or abnormal shedding
  • excessive drinking and urination
  • excessive sweating
  • weight loss and muscle atrophy
  • depression and poor performance
  • normal to increased appetite
  • fat deposits along the crest of the neck, over the tail head and above the eyes
  • laminitis (chronic, recurrent)
  • lowered immunity - chronic infections or slow wound healing

Hypothyroidism - low thyroid production by the thyroid gland leading to a low metabolic rate and weight gain.

Symptoms of EMS:

Insulin resistance - The liver, skeletal muscles and/or fat cells don't respond to insulin so rather than glucose being used for work, it circulates in the blood and more insulin is discharged by the pancreas.
Mild laminitis
Usually affects horses between 8-18 years.
All breeds can be affected though more susceptible are ponies, Morgans, Pasos, and Warmbloods.
Fat accumulation on the crest of the neck, over the shoulders and just above the tailhead, or in the sheath of geldings.
Erratic estrous cycles in mares.
Obese, easy keepers (even those on sparse grass hay only diets).


Glucose tolerance test performed by a veterinarian.
Thyroid test to eliminate Hypothroidism.
Dexamethasone Suppression test and/or Domperidon test (blood tests) to eliminate Cushing's Syndrome.


In humans, causes include aging, pregnancy, smoking, reduced physical activity, and obesity. Insulin resistance can lead to Type 2 Diabetes.
In horses, it is not known, but it could be a combination of genetic or environmental factors, most probably obesity and lack of exercise. (Sound familiar?)
Meals high in starch and sugar lead to spikes in blood glucose and insulin and subsequently to insulin resistance.


Weight reduction reduces cortisol (and other hormones). Lower cortisol levels lead to increased insulin sensitivity, or a more normal glucose-insulin relationship.
No grain, molasses.
Extremely judicious pasture grazing program, perhaps none.
Protein, mineral and vitamin supplement as needed, especially anti-oxidants such as Vitamin E
Corn oil or rice bran as needed for energy.
Exercise program
There is no medication suitable for treatment - however veterinary experts suggest using a supplement containing chromium, magnesium or vanadium to increase insulin sensitivity. Refer to Neutraceutical box.


Don't feed grain unless it is required for a specific situation.
Don't feed grain in large quantities to any horse and especially not to young horses.
Keep horses at a healthy weight.
Provide regular exercise.


Since there is no medical treatment for EMS, manufacturers of neutraceuticals have put together blends of various vitamins, minerals, herbs and other substances, some of which show promise. Here are some of the products that are said to be of possible help to maintain proper metabolism and help regulate glucose and insulin levels while helping with digestion and nutrient absorption. While none of these have been tested or proven to be helpful, you'll probably recognize many substances that are currently recommended for humans with similar conditions.

Antioxidant Vitamins A, C, D, and E and
Grape Seed Extract and Alpha Lipoic Acid (antioxidants)
Niacin, Folic Acid, Biotin
Siberian Ginseng
Ginger Root

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