Icelandic Horse Connection

Insulin Resistance

Fairly recently, isulin resistance (IR) has been recognized in horses and ponies (ponies being more prone to it). The IR horses were originally diagnosed as cushings horses, but they didn't really fit the general profile of being older, laminitic, with curly unshedding coats.

They tend to get cresty with unusual fat deposits on their sides or tail head. They were labeled "omental cushings" because of the omental-type fat, but now are being called IR (insulin resistant) horses.

Here's a picture... look at the side of the horse and in the area of the middle of the ribs... do you see the round blob of unusual fat?

omental fat

My horse previously had been normal sized, receiving 3 large flakes per day of bermuda. Due to our move, and having to be boarded, she received 2 smaller flakes of oat hay per day. Seems like she might have lost weight, but she gained! The culprit was the oat hay.

For more information, please see the EquineCushings email list: EquineCushings. The files section has several important documents, as well as some in the archives of the GaitedHorse list.

Dr. Evelyn Kellon is a wonderful resource for information on this subject.

In SOME overweight people with metabolic syndrome / insulin resistance / type II diabetes, a change has been found in the way the fat cells in the abdomen handle cortisol (the omentum is the tissue that covers the abdominal organs. It contains fat). The result is an increased cortisol effect, a result of which is insulin resistance.

Whether this chance occurs after these people get overweight or is the cause of their becoming overweight is not clear. There is THEORY that insulin resistance in horses may have the same mechanism.

However, in people with this problem they classically only have heavy fat deposits around the abdomen, not arms, legs, neck, etc.. The horses get fat deposits all over. Also, this is far from the only cause of insulin resistance in people and other animals so even if it is eventually found to also occur in horses it probably won't be accurate to suggest every horse with insulin resistance has omental Cushings. For example, it's been known for close to 30 years that ponies are more insulin resistant than horses - and this includes normal ponies too, not just fat laminitic ones. It may very well be just part of their normal metabolic make up, not a "disease" per se.

Cushings by the way just means an overproduction of active cortisol. In the horse, the only proven cause of this is a pituitary tumor. It could also happen from an adrenal gland tumor or problem with how the cortisol is metabolized.

It would be nice if we could fit every horse into a little box, be able to say that if it's not a pituitary tumor producing insulin resistance it must be peripheral Cushings. Probably won't turn out to be that simple though. The good news is that regardless of what is causing the insulin resistance the management changes to control it are the same - regular exercise, low NFC diet, avoidance of extremes of fat or protein intake and mineral balancing. These things are absolutely essential for good control, regardless of whether it's just the individual's basic metabolism or is caused by a pituitary tumor. Even the drugs for controlling Cushings/pituitary tumor hormonal outputs won't completely control it without management changes.

One of the genetic researchers who is investigating breed associated disease tendencies, comments: The first concept is "multi-generational environmental conditioning (MGEC)." This may be related to a possible "sugar / fat intolerance." MGEC can become significant when you have a constant environment for hundreds of years. The baby in the womb is being "genetically programmed" for its outside world. Is there a lot of food out there, or is food a little grass and weeds growing along the canal and a few dried corn stalks every once in a while? For hundreds of years this breed may have been conceived, born, reproduced and died in the latter environment.

When viewed from a multi-generational aspect, in an austere environment, an easy keeping breed can turn into a "rich diet" intolerant breed. Some portions of the population can handle rich diets, some portions of the population will be intolerant of rich diets and some portions of the population will develop and transmit a genetic INABILITY to metabolize a rich diet. The spectrum of response is ability, tendency, intolerance, and inability. The inability manifests as a disease which has a genetic component. However a significant comment is that the degree of expression is influenced by both genetic and environmental factors. He went on to name numerous documentated cases of this factor in the human population.<<

More info on feeding IR horses: Beet Pulp as a Supplement

Two alternative feeds for IR Horses: Triple Crown Safe Starch Forage, or: Ontario Dehy Inc. Timothy-Balance Cubes.

Temporary IR Diet: Temporary IR Diet

Treats: Skode's Horse Treats http://www.SkodesHorseTreats.com

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