Horse Health Article - Equine Metabolic Syndrome

Equine Metabolic Syndrome (EMS) is one of the most frequently studied medical conditions occurring in horses over the last 5 years - and rightly so, as it is responsible for the vast majority of laminitis cases in equines.

So what is EMS, what causes it, how does it cause laminitis, and what are the latest in available treatments? Read on to find out.

What is Equine Metabolic Syndrome (EMS)?

EMS, or Equine Metabolic Syndrome, is a genetic condition occurring in particular breeds of horses which predisposes them to developing laminitis. Commonly affected breeds include Warmbloods, Arabians, Quarter Horses/Paints and pony breeds.

Researchers attribute the genetic association to “thrifty genes,” which allowed horses to maximise their efficiency of obtaining nutrients from minimal feed availability in times of drought or heavy snow conditions, where feed was scarce. However, in our modern horses where feed is in abundance - this genetic programming does not work in our favour!

EMS is characterised predominately by insulin dysregulation, which means that the horse’s body has irregular insulin pathways compared to a normal horse. Examples of insulin dysregulation include insulin resistance, or excessive insulin levels (hyperinsulinaemia) either at rest or after eating (post-prandially.) High concentrations of insulin in the blood in horses with EMS cause the lamellar attachments within the feet to swell and detach = laminitis.

There are two main phenotypes of EMS: the obese type (the “good doers”) and the lean type. It is important for horse owners to understand that while obesity can be a sign of EMS, lean horses may also have EMS - meaning that you cannot rely on body type alone to rule out whether your horse could have EMS.

Clinical Signs of EMS

The most common clinical signs of EMS may include:

• Weight loss resistance (e.g. “good doers”)

• Abnormal fat deposits - cresty neck, fat deposits under the skin (e.g. over the ribs/shoulders/at the tail base)

• Changes in hoof growth (e.g. divergent hoof rings.)

• Laminitis

Diagnosis of EMS

Not all horses with EMS will have basal hyperinsulinaemia (high blood insulin levels at rest), therefore relying on a basal insulin as a diagnostic rule-out for EMS may lead to false negatives - as some horses will only show hyperinsulinaemia after eating.

Therefore, a diagnosis of EMS is best achieved using a blood test for insulin levels following the administration of sugar syrup known as the Oral Sugar Test. This requires oral administration of specified quantity of sugar syrup 60 minutes prior to obtaining blood in order to test for abnormally increased insulin levels.

Horses with EMS will have an abnormal insulin response (elevated insulin level) in response to glucose being absorbed from the gut when compared to normal horses.

This test can also be done using in-feed glucose powder, however at Cape Equine we prefer the oral sugar test, due to the guaranteed ingestion of the required testing material (as some horses won’t eat the glucose powder in-feed due to poor palatability.)

Medications for EMS

The mainstay of treatment for EMS should always be environmental and dietary management first and foremost. However, in some horses despite receiving adequate dietary restrictions and undergoing regular exercise - their insulin concentrations still remain high.

In these circumstances, medications may be used to assist in treatment.

Metformin hydrochloride is a medication that acts on the enterocytes (intestinal cells) to suppress glucose absorption. It is not well absorbed when given orally in the horse, so it must be given on an empty stomach 30-60 minutes prior to feeding in order to be most effective. It is usually given every 12 hours.

Levothyroxine is another medication that we can use in the management of EMS. It accelerates the metabolic rate (rate at which the body conducts its normal processes), and therefore encourages weight loss.

Weight loss is important for EMS, as adipose (fat) tissue has been shown to correlate with increased insulin levels. Levothyroxine is given orally once a day until an improvement in body condition score is noted, or for a maximum of 6 months at a time. Horses are gradually weaned off the medication to allow their body to “return to normal.”

Recently, equine veterinarians have started to utilise human medications known as SGLT-2 inhibitors to treat horses with EMS. These medications work by causing the kidneys to excrete glucose into the urine, therefore causing a subsequent drop in insulin levels.

Erutgliflozin, a human SGLT-2 inhibitor is being used in horses with great success, however the use of this medication requires repeated follow-up blood tests to ensure the horse’s long-term safety, as these medications are currently not registered for use in horses. The known side effects of Ertugliflozin include polyuria/polydipsia (excessive urination/drinking) and elevated blood triglycerides (hypertriglyceridaemia).

Exercise is hugely important for the maintenance of horses with EMS

Diet & Exercise for EMS

Horses with laminitis should not be exercised if their feet are actively inflamed, as this can make the laminitis worse. However if your horse is not acutely laminitic, and you have approval from your veterinarian, exercise is one of the main ways that we treat EMS in horses.

Exercise encourages the absorption of glucose from the bloodstream by myocytes (muscle cells), leading to less glucose circulating in the bloodstream, consequently lowering the horse’s insulin levels.

In horses with stable hoof lamellae (i.e. horses that have fully recovered from laminitis), the minimum exercise recommendation is unridden fast trot to canter for 30 minutes on a soft surface, a minimum of three times per week.

Dietary management of horses with EMS can be difficult. The aim of any EMS-diet is to decrease the amount of sugar available to the horse to decrease the amount of sugar available in the horse’s diet.

The digestive system of the horse works differently from ours in that there are two types of digestion that occur: foregut digestion (stomach/small intestinal) and hindgut digestion (caecum/large colon) digestion.

The majority of foregut digestion comprises the breakdown of starch, non-structural carbohydrates (NSCs), proteins and fats. Hindgut digestion, performed by the microbes within the horse’s large colon and caecum, breaks down fibre into volatile fatty acids (VFA’s) - which act as a direct energy source for horses.

By reducing the amount of starch and non-structural carbohydrates in the diet, we are able to minimise foregut digestion of these molecules into glucose, and therefore limit the horse’s insulin response to these feed types (remember, less glucose = less insulin.) The current recommendation is that all forages provided to the horse (e.g. grass/hay) should be less than 10% NSC.

As such, EMS diets should be rich in fibre (in order to maximise hindgut digestion) and low in starch/NSC. As a general rule, fats in the diet should be minimised, as adipose tissue can release inflammatory enzymes which can worsen the symptoms of EMS.

Depending on the horse’s performance requirements, protein levels in the diet may need to be increased in order to supplement energy and maintain musculoskeletal development.

We recommend horse owners consult a qualified Equine Nutritionist for their horses in order to make the diet as “easy” as possible for their lifestyle and their horses’ individual requirements.

Reference List:

1.  Frank, N. et al., 2020. Recommendations for the Diagnosis and Treatment of Equine Metabolic Syndrome (EMS). Equine Endocrinology Group.

2.  Durham, A. et al., 2019. ECEIM consensus statement on equine metabolic syndrome. Journal of Veterinary Internal Medicine, 33, 335-349.

3.  Morgan RA, McGowan TW, McGowan CM. Prevalence and risk factors for hyperinsulinaemia in ponies in Queensland, Australia. Aust Vet J. 2014;92(4):101-106.

4.  Grenager, N., 2021. Endocrinopathic Laminitis. Veterinary Clinics of North America: Equine Practice 37, 619-638.