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Insulin Resistance

Also known as Metabolic Syndrome (EMS)

What Is It?

A syndrome of obesity, insulin resistance and Laminitis.

Insulin is a hormone made by the body, its purpose is to tell the many cells of the body to utilise the sugar (glucose) in the blood which has been obtained from food. For example, insulin tells the body’s cells to either use it for energy right now, or to store it as fat. Animals which are constantly eating (such as the horse that should be foraging for at least 14 hours in every 24) are therefore going to be constantly producing insulin.  

Insulin resistance is a condition where the many different types of cells in the body gradually start failing to respond to insulin. (Very similar to Type II Diabetes in people). This means the glucose in the blood cannot be processed or stored, so the blood glucose then becomes high. The body responds by increasing the production of insulin – insulin levels in the blood stream become much higher than normal and the effects this has on tissues in the body can lead to Laminitis.  

This failure of cells to respond to insulin can be due to a genetic predisposition or an acquired condition due to obesity. In an obese horse, the body is constantly trying to store all the glucose it is obtaining from food. However, a complicated relationship between insulin and another hormone, leptin, affect the cells’ ability to respond to the glucose and the cells start to become resistant to insulin’s signal.

Whilst obesity is a major predisposing factor for insulin resistance, there are highly susceptible breeds such as native pony breeds, where there is likely to be an underlying genetic predisposition. Other breeds can somehow be quite remarkably obese with normal insulin sensitivity.

The disease “Cushings” can also cause insulin resistance in many horses or ponies. See our separate fact sheet about this common disease affecting older horses or ponies.

Obesity In Horses

Equine Metabolic syndrome is the term used to describe a pony with this insulin resistance and the detrimental effects caused by excessive insulin in the blood stream. High levels of insulin will cause Laminitis. The exact mechanism by which Laminitis is caused by insulin has not been fully determined. However, its certainty of causing Laminitis has been proven following a study where 100% of a group of healthy equines – some normal and some fat in body condition – injected with high levels of insulin developed Laminitis!

Clinical Signs of EMS

  • Obesity.
  • Laminitis.
  • Unusual distribution of fats e.g. belly fat, crest fat.

Diagnosis

A blood test for baseline insulin levels will identify approximately 80% of cases.

Many cases of insulin resistance are identified with this test. However, if the result is borderline, a more dynamic test should be performed. There are two tests that can do this, the simplest test being the oral glucose stimulation test.

The oral glucose stimulation test involves a base line blood test to have been taken to check ‘resting’ levels of insulin and then a second blood test is taken, 2 hours after a sugary feed (containing dextrose) has been fed to the horse. Equines with equine metabolic syndrome will have an exaggerated response – produce much higher than normal levels, of insulin into the blood stream.

Treatment

Weight loss and fat cell reduction through diet and exercise is the mainstay for treatment of this condition, as well as tests to check for the presence of the disease “Cushings”.

A reduction of total calorie intake as well as basic carbohydrate intake is crucial.

Soaking hay for at least one hour is also essential. Soaking hay acts to dilute out the starch and sugar content. Every case is different and we will tailor the diet specifically to your horse. However, as a rough guideline, to achieve weight loss in an obese horse the initial aim should be to feed 1-1.5% of the horse’s body weight as dry forage daily. The total quantity of hay is measured out as dry matter before it is soaked. For example, a 400kg pony should be fed 4-6 kg of hay (which should then be soaked for a minimum of 1 hour) per 24 hours as a maximum. Any additional feed such as low calorie chaff containing vitamins and minerals, is weighed out and subtracted from the total daily allowance, e.g. 1kg of chaff fed split between 2 feeds, should leave a 400kg pony having 3-5kg of hay in 24 hours.

After an acceptable body weight has been reached, depending on your vet’s advice, the quantity of feed may increase but it never should go above 2- 2.5% of the horse’s body weight as a daily ration.

Metformin is a medication which has variable results in treatment of insulin resistance. Its effects are thought to include creating increased insulin sensitivity in tissues and decreased production of glucose by the liver. It also is thought to block glucose absorption by the gut. Whilst its effects are still debated, it remains one of the only medicines we can use to treat this condition.

A very recent study has found metformin to be most useful in the later stages of treatment of insulin resistance. The use targeted in the study was for the period of time after the horses have been dieted and reached a goal weight. It was found to be beneficial as a treatment for horses that are starting to return to a more normal life and beginning to be reintroduced to small amounts of grazing again.

Much more research is still needed. Metformin has been thought to be successful in some horses, but not in others such as obese mares which are reported to be least responsive. There are a variety of low calorie enrichment ideas suitable for the EMS-risk pony.

Practice information

Chobham

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