Article by: Philip J. Johnson, BVSc, MS, MRCVS, DACVIM

Affected horses tend to be aged between 6-to-20 years and there does not appear to be a sex predilection. The problem is reported more commonly in some pony breeds, domesticated Spanish mustangs, Peruvian Pasos, Paso Finos, European Warmbloods, American Saddlebreds, and Morgan horses. Affected horses are commonly obese and develop excessive adiposity at specific locations, especially in the crest of the neck, at the shoulders, above the gluteal muscles, and in the sheath (geldings). Female horses are notoriously difficult to breed and exhibit abnormal ovarian cycling behavior. Horse owners refer to many of these horses as "easy keepers" and vigorously contend that all efforts to reduce the horse's obesity by dietary restriction are futile. Ample intra-abdominal (omental) adiposity is evident during ultrasonographic examination of the abdomen or at necropsy of affected horses.

Many of these horses are presented to veterinarians for diagnosis of lameness attributable to laminitis. There is a very strong association between the development of obesity, metabolic syndrome and the risk for developing laminitis. Commonly, at initial veterinary examination, there already exists both physical and radiographic evidence for long-standing laminitis in these horses although reputable and credible owners and managers report that there have been no prior signs of laminitis or any obvious explanation. Metabolic syndrome is often recognized incidentally when horses are presented for other reasons, such as routine health care or other medical problems. In these horses, visible changes in the hoof that are commonly attributable to laminitis (including prominent growth lines, palmar divergence of growth lines, and a convex sole) may be evident in the absence of laminitic pain or any history of laminitis or lameness. There are minimal hematological changes in horses affected with metabolic syndrome (unless laminitic pain is prominent). Abnormal results of routine serum biochemical profiling might include a slight-to-moderate elevation in the glucose and triglyceride concentrations.