Metabolic Predispositions to Laminitis in Horses and Ponies: Obesity, Insulin Resistance and Metabolic Syndromes

Equine veterinarians have long recognized an association between metabolic abnormalities, notably obesity and insulin resistance (IR), and increased risk for laminitis in horses and ponies. Recent observational studies have provided evidence that an insulin-resistant phenotype is strongly linked with a predisposition to laminitis. Although descriptions of this laminitis-predisposed phenotype have varied, in general there is a clustering of obesity (generalized or localized), IR, hyperinsulinemia, and hyperleptinemia. The observation that laminitis can be induced in healthy ponies by maintaining supraphysiologic circulating insulin (1,000–1,100 mU/L) concentrations for 2 to 3 days suggests that hyperinsulinemia may play a direct role in the pathogenesis of laminitis in susceptible animals. Therefore, laminitis may be triggered in a chronically insulin-resistant horse or pony under conditions that exacerbate IR or hyperinsulinemia, for example, the grazing of pasture with high nonstructural carbohydrate content (eg, during spring or when pastures are stressed by drought or frost), consumption of other feeds rich in starch and sugars (grains, sweet feeds), overfeeding that induces or worsens obesity, and the administration of corticosteroids. Identification of insulin-resistant horses and ponies at high risk for laminitis facilitates preemptive avoidance measures with a focus on strategies that (1) improve insulin sensitivity (eg, caloric restriction, increased exercise, judicious use of pharmacologic agents [levothyroxine sodium, metformin]) and (2) minimize exposure to environmental factors that increase risk of laminitis (elimination of grains and sweet feeds from the diet, restricted access to pasture during high-risk periods such as spring).