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Insulin resistance in horses

Dave Wright, DVM, Buffalo Equine

Equine metabolic syndrome or Insulin Resistance is gaining a great deal of publicity. It is a disorder of carbohydrate metabolism that is typically seen in overweight middle-aged horses and ponies, and is often associated with severe laminitis. Many horses that develop the metabolic syndrome are easy keepers. These horse often build up a high level of a stress hormone called cortisol. Among its many metabolic effects, increased circulating levels of cortisol increase blood sugar (glucose) and also inhibits the uptake of glucose into cells by antagonizing the action of insulin. Persistent high blood sugar is known to be toxic to blood vessels in humans and it may be that high blood sugar contributes to laminitis in horses and ponies by damaging the blood vessels in the hoof.

Metabolic syndrome needs to be distinguished from Cushing's Disease and a veterinarian needs to do a number of blood tests to make this distinction. Resting insulin and blood sugar are probably the most common screening test used to diagnose the metabolic syndrome. Blood must be taken following a minimum 5 hour fast and the horse should not be stressed or in pain at the time.

Metabolic Syndrome can only be managed through diet and exercise; no drugs have been shown to improve the condition. It can be prevented by a weight control program. Pick up a weigh tape and begin monitoring your horse. If the horse is overweight, begin an appropriate diet. Obesity is a major cause of insulin resistance. Feed only grass hay or grass alfalfa mix, with no grain. It is better to feed smaller quantities more often than to feed only one or two large feedings. Feed a trace mineral block, a loose mineral salt, or a ration balancer with the hay.

If you suspect that your horse has laminitis due to metabolic syndrome, it is a good idea to schedule a physical exam. Radiographs can determine the severity of the laminitis and a series of blood tests can confirm an association with metabolic syndrome. You can also test your hay to determine its carbohydrate content. Timothy hay and mixed prairie grass hay is generally better than brome. Straight alfalfa is never appropriate for these horses.

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