The Facts on Insulin Resistance
by Beth Stelzleni, MS, PAS of Mars Horsecare US, Inc.
Talk to any equine vet around today, and one thing they might tell you is that insulin resistance is on the rise. This disorder is occurring in much higher number today than it ever has been. Insulin resistance is a major risk factor for laminitis, which can be a very painful, possibly deadly disease for the horse. By understanding exactly what this disease is and what causes it, horse owners can reduce the risk that their horse will become one of the many affected by it.
To understand insulin resistance, it’s helpful to first understand how insulin works in the normal body. In any animal, after a meal is eaten the food is converted into glucose, or a simple sugar used for energy in the body. This glucose travels in the animal’s bloodstream to various muscles and organs, where it can be used for energy to fuel vital life processes. In a normal horse, insulin’s job is to “grab” the glucose molecules from the bloodstream and pull them into the cells of whatever tissue may need them. In an insulin resistant horse, the insulin can’t grab hold of the glucose molecules. Because the insulin can’t move the glucose from the bloodstream into the tissues, blood glucose stays high and never returns to a normal, pre-meal level. In an effort to fix this problem and reduce blood glucose, the body secretes more and more insulin to try to remove glucose from the blood steam. It’s these high levels of blood insulin that result from insulin resistance that cause so many health problems for our horses.
Horses most at risk for insulin resistance include those that have Cushing’s disease and those that are older, or senior horses. Many of the horses that fit these categories are overweight, and obesity is a major risk of insulin resistance. What are especially dangerous are the horses who are not only obese, but who show obvious fat deposits in certain key areas. Abnormal, lumpy fat deposits at the base of the tail, behind the shoulders and along the crest of the neck are referred to as “regional adiposity” and are a sure warning sign of insulin resistance.
If you have a horse that has insulin resistance, or one that is at risk, the first mode of action you need to take is to make sure the horse is at a healthy bodyweight. If your horse is overweight, it’s important that you implement a weight reduction program (see “Overweight and Under Concerned?”). It’s also important that obese horses are started on an exercise program. Exercise not only help reduce body weight but can also improve the efficiency of how insulin works in the horse’s body.
For any insulin resistant horse, whether overweight or not, the key rule for the horse’s diet is to reduce the starch and sugar consumed by the horse. To do so, an owner should choose low starch and sugar grain mixes. A ration balancer is an excellent option for IR horses, as they are very low in starch and sugar but also low in calories to help control bodyweight. It’s important to also choose a grain mix with a very low feeding rate, as the pounds of starch and sugar the horse consumes per day is much more important that the actual percentage. For example, a feed that is 10% starch and sugar may sound like a good feed for and IR horse, but if the recommended feeding rate is at least 10 pounds per the actual amount of starch and sugar consumed per day will be too much.
Forage is vital to the health of all horses, but must be closely monitored in an IR horse. Fresh green grass can be quite high in sugar, so the consumption of this type of pasture by IR horses needs to be controlled. These horses can either be fitted with a grazing muzzle or turned out in a dry lot to control their grass intake. When choosing hays, owners should look for a more mature, stemmy hay, as these hays are usually lower in starch and sugar then younger hays.
