Insulin resistance

A SILENT KILLER

Insulin resistance is, unfortunately, an increasingly common problem in our equine population but is often overlooked or missed by owners. The sad reality is that often we only spot it very late, by which time damage has likely occurred. If, when reading this, you recognise any of the symptoms we describe as being present in your equine companion, please speak to your vet as a priority. This condition can lead to laminitis if left untreated, and whilst insulin resistance in itself is not life-threatening, laminitis certainly is.

WHAT IS INSULIN RESISTANCE?

Insulin resistance is a condition in which the body’s tissues have a decreased responsiveness to the hormone insulin. Insulin is an essential hormone for the body, as it regulates glucose metabolism. Insulin instructs the body to take glucose from the bloodstream into the tissues to either make use of the glucose immediately for energy or to make it into the bigger molecule of glycogen which can be stored in the tissue for later use.

In healthy tissues, insulin binds to receptors on the tissues, which send a signal that stimulates the cells to take up glucose from the bloodstream. However, the receptor doesn’t work as it should in insulin-resistant tissues. This results in the signal not being transmitted through the tissue and glucose not being removed from the bloodstream. The blood glucose level remains high, which signals the body to produce more insulin to try to get the tissues to take up glucose. Ultimately, this results in hyperinsulinaemia (a condition where insulin levels are permanently too high) and even more health issues than high glucose alone.

WHAT CAUSES INSULIN RESISTANCE?

The exact causes of insulin resistance are unknown, and this subject, in itself, can be quite controversial. Some vets believe the condition is not a disease but merely a genetic variant in the metabolism of affected horses. These vets think the condition is similar to any other allergy a horse could have in that they are allergic to certain high sugar and starch foods. In their view, the horse is born with the condition and must just be managed accordingly.

Other vets, however, believe that there are risk factors that lead to the development of the condition in genetically predisposed horses. This means that certain horses are more at risk genetically, such as Arabians and pony breeds, but it takes one of the following risk factors to also be present for the condition to manifest. These risk factors include the following: • Obesity – This is widely believed to be the biggest risk factor. • Old age – Horses over the age of 20 are more at risk. • Diet – Feeding a diet high in simple sugars and starches is believed to be a risk factor independent of obesity.

NOTE: Some vets believe that it is actually feeding a diet high in simple sugars and starches that causes the horse to develop the condition, not just makes the condition worse.

SYMPTOMS

The symptoms of insulin resistance are relatively nonspecific, but if you notice even one or two of these in your horse, it is worth discussing with your vet. These symptoms include, but are not limited to:

• Obesity • Abnormal fat deposits, usually on the crest, rump and above the eye. Some horses also have a fatty sheath or udder. • Excessive urination • Thirst • Low energy levels • Muscle wasting • Loss of body condition • Laminitis

TESTING

Lab testing for insulin resistant horses shows elevated insulin concentration or abnormal changes in blood insulin or glucose concentrations when the horse is given extra glucose or insulin as a stimulus. Several tests have been developed along these lines to investigate insulin resistance. Your vet can tell you which test is most appropriate in your particular case.

TREATMENT

As with everything, prevention is the best cure, and although some vets believe the condition cannot be entirely prevented, minimising the risk factors will benefit all cases.

Feeding a proper diet, ensuring your horse gets plenty of exercise and maintaining a healthy body condition score all reduce the risk of developing the condition.

If your horse is already insulin resistant, changing diet, increasing exercise levels (providing laminitis is not present) and arranging regular farrier visits are the best ways to maintain quality of life and reverse any changes that have occurred. Feeding foods with a low glycaemic index, like beet pulp and soaked grasses, also helps to lower blood glucose and insulin. Your vet may want to try your horse on medication, but the management changes will normally be implemented first.

The good news is that by incorporating exercise and the dietary recommendations into your horse’s life, you should be able to keep him happy and healthy for many years to come.

DIETARY CHANGES

The primary management of insulin resistant horses is dietary. Horses with the condition should be fed a low-carb, low-fat and mineral-balanced diet. Any sugarladen concentrate feeds or time spent on lush pastures should be reduced, until they are fully eliminated from the horse’s routine. The gradual reduction is important to avoid shocking the horse’s system, another trigger for laminitis. Your horse will need to be kept away from high-sugar pastures and concentrate feeds until all signs of the condition are absent, and your vet feels your horse can be reintroduced to them with caution. Sadly, some horses will never be reintroduced as their condition is simply not stable enough.

It goes without saying, of course, that whilst lush grazing and and high-sugar concentrate feed are removed, grass must be supplied to horses 24/7. The grass can be soaked to reduce sugar levels or fed in slow feeders, but horses must never be without something to chew on. Reducing the amount of grass fed or leaving your horse without grass for many hours will ultimately cause problems like colic that are immediately life-threatening and also precipitate a stress response, potentially resulting in ulcer formation and laminitis.