Insulin resistance (IR) is becoming increasingly common in our equestrian population but is often overlooked by owners. If after reading this you recognise any of the symptoms in your own horse, we highly recommend you speak to your vet as a priority. This condition can quickly lead to laminitis, if left untreated, and whilst insulin resistance in itself may not be life-threatening, laminitis certainly is.
What is it?
Insulin resistance is a condition in which body tissues have a decreased responsiveness to the hormone insulin. Insulin is a very important hormone for the body, as it regulates glucose (sugar) metabolism. Insulin instructs tissues to take in glucose from the blood stream after eating and stimulates these tissues to either use that glucose immediately or to make it into the bigger molecule of glycogen, which provides a way of storing the glucose and therefore, energy.
In healthy issues, insulin binds to receptors on the tissues, which send a signal that stimulates the cells to take up glucose from the bloodstream. However, in insulin-resistant tissues, there is a problem that occurs with the signal after the insulin molecule binds to the receptor. This problem means that the signal is not properly sent through the tissue, and glucose is not taken up out of the bloodstream and into the tissue. This causes the blood glucose level to remain high, which is a signal for the body to produce more insulin to try to get the tissues to take the glucose in. This can lead to hyperinsulinaemia (a condition where the insulin level is high all of the time), which can cause even more health issues than the high glucose levels alone.
The exact causes of insulin resistance are not known and this subject is, in itself, quite controversial. Some vets believe the condition to not be a disease, at all, but merely a genetic variant in the metabolism of these horses. These vets believe that the condition is similar to any other allergy a horse could have, in that they are allergic to certain kinds of high sugar and starch foods. They believe the horse is born with the condition and that the condition must just be managed.
However, others believe that there are risk factors that lead to the development of the condition, in genetically predisposed horses. What this means is that certain horses are more at risk genetically, but that it takes one of the following risk factors to also be present for the condition to actually develop. These risk factors include the following:
- Obesity – which is widely believed to be the biggest risk factor.
- Old age – horses over the age of 20 are more at risk.
- Breed – certain breeds like the pony breeds and Arabians are thought to be more predisposed.
- Diet – 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.
The symptoms are relatively non-specific, but if you notice even one or two of these in your horse you should discuss them with your vet. These symptoms include:
- Abnormal fat deposits, usually on the crest, rump and above the eye. Some horses also have a fatty sheath or udder.
- Excessive urination
- Low energy levels
- Muscle wasting
- Loss of body condition
If you suspect your horse may have insulin resistance, you should contact your vet immediately.
Lab testing for IR horses shows elevated insulin concentration or abnormal changes in blood insulin or glucose concentrations when the horse is given extra glucose or insulin. Several tests have been developed to investigate IR. Your vet will be able to tell you which test is most appropriate in your case.
As always, prevention is the best cure. Feeding a proper diet, ensuring your horse gets plenty of exercise and maintaining a healthy body condition score of 5-6 all reduce the risk of your horse developing the condition.
However, if your horse is already insulin resistant, changing diet, increasing exercise levels (providing laminitis is not present) and arranging regular farrier visits is the best way 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 help to lower blood glucose and insulin. Your vet may also want to try your horse on medication, but normally the management changes are tried first.
By adopting the diet and exercise levels accordingly, you should be able to keep your horse happy and healthy for many years to come.
The primary treatment of IR horses really is dietary. Horses with IR should be fed a low-carb, low-fat and mineral-balanced diet. Any concentrate feeds or time spent on lush pastures should be eliminated until all signs of the condition are totally absent and your vet feels your horse can be reintroduced to them with caution. It is important, however, to also note that whilst removing concentrate feed and access to lush pasture is essential, grass/hay should always be fed as usual. ‘Starvation measures’ like cutting the quantities of grass fed are not an option, and in fact the stress caused by these methods makes the insulin resistance worse. Horses and ponies need constant (24/7) access to grass as their digestive systems are designed for them to be trickle feeders. All grass must just be soaked first to remove the excess sugars, and perhaps fed in a slow feeder if obesity is a concern but removing grass for even brief periods is not an option.