Equine Metabolic Syndrome

The images in Figures 1 and 2 are of an obese donkey. If you follow the dark, dorsal stripe you will notice that the withers of this donkey completely falls to the left side due to the large concenetration of fat that has accumulated within this area!! This condition is also termed "cresty neck".  In Figure 2, the abnormal fat accumulation over the donkey's top line is apparent as is the large deposit of fat just in front of the tail head region! Although slightly humurous, this condition presents a serious medical problem for this donkey. The abnormal accumulation of fat in the area of the neck, top-line, tail head and internally can predispose donkeys and horses to a condition known as metabolic syndrome.

Figure 1

Figure 2

Metabolic syndrome occurs most commonly in over-conditioned horses but has a species predilection for Morgans horses, Arabian horses, Tennessee walking horses, and ponies. The condition is some what similar to adult onset diabetes in humans, which also results in a state of insulin resistance. The serious and some times deadly complication of metabolic syndrome is laminitis!! (Figure 3 and 4). The association between insulin resistance and laminitis is not well understood however in humans with adult onset diabetes, the high circulating levels of glucose are toxic to blood vessels and may cause loss of limb due to poor perfusion. This has not been proven in horses but sounds very similar to what happens in the case of laminitis!  These cases typically present to me AFTER the horse has already foundered and there is a long history (6-24 months) of intermittent lameness, coffin bone rotation, and recurrent foot abscesses!! In my experience, these horses will NOT improve until the insulin resistance is documented and treated!! Unfortunately, if the condition is not diagnosed early enough, severe coffin bone rotation may occur resulting in protrusion of the coffin bone through the bottom of the foot and humane euthanasia (Figure 3 and 4) !

Figure 3

 

Diagnosis simply involves a blood sample collected from a fasted animal that compares the level of glucose and insulin simultaneously! Occasionally, a glucose challenge may be necessary to establish that a horse is glucose intolerant and insulin resistant. Once diagnosed, the treatment involves regulating the caloric intake of the animal and medical management with thyroid hormone supplement. It is very important to understand that these horses do NOT have a thyroid deficiency!! We are merely increasing the metabolic demand by treating with thyroid hormone supplementation and forcing the animal to lose body fat!!  In addition, to the medical management, the caloric intake is carefully regulated between limited pasture access and low starch diets. Finally, the farrier plays a integral part in helping those horses that have foundered due to the metabolic syndrome. Interestingly, these horses often remain tender-footed regardless of the type of shoe UNTIL the insulin resistance is properly regulated. 

You can read more about equine metabolic syndrome at:

http://www.aaep.org/health_articles_view.php?id=268

http://www.thehorse.com/free-reports/29993/equine-metabolic-syndrome