Effects of diet-induced weight gain on insulin sensitivity and plasma hormone and lipid concentrations in horses

Objective-To determine the effects of diet-induced weight gain on glucose and insulin dynamics and plasma hormone and lipid concentrations in horses. Animals-13 adult geldings. Procedures-Horses were fed 200% of their digestible energy requirements for maintenance for 16 weeks to induce weight gain. Frequently sampled IV glucose tolerance tests were performed before and after weight gain to evaluate glucose and insulin dynamics. Adiposity (assessed via condition scoring, morphometric measurements, and subcutaneous fat depth) and plasma concentrations of insulin, glucose, nonesterified fatty acids, triglycerides, and leptin were measured on a weekly or biweekly basis. Results-Mean +/- SD body weight increased by 20% from 440 +/- 44 kg to 526 +/- 53 kg, and body condition score (scale, 1 to 9) increased from 6 +/- 1 to 8 +/- 1. Plasma glucose, triglyceride, and nonesterified fatty acid concentrations were similar before and after weight gain. Leptin and insulin concentrations increased with weight gain. Mean SD insulin sensitivity decreased by 71 +/- 28%, accompanied by a 408 +/- 201% increase in acute insulin response to glucose, which resulted in similar disposition index before and after weight gain. Conclusions and Clinical Relevance-Diet-induced weight gain in horses occurred concurrently with decreased insulin sensitivity that was effectively compensated for by an increase in insulin secretary response. Obesity resulted in hyperinsulinemia and hyperleptinemia, compared with baseline values, but no changes in lipid concentrations were apparent. Preventing obesity is a potential strategy to help avoid insulin resistance, hyperinsulinemia, and hyperleptinemia in horses. (Am J Vet Res 2009;70:1250-1258)