Effects of exercise training on adiposity, insulin sensitivity, and plasma hormone and lipid concentrations in overweight/obese, insulin resistant horses

Objective - To determine effects of exercise training without dietary restriction on adiposity, basal hormone and lipid concentrations and glucose and insulin dynamics in overweight or obese, insulin-resistant horses. Animals - 12 overweight or obese (body condition score ≥ 7), insulin-resistant (insulin sensitivity ≤ 1.2 × 10-4 L/min/mU) geldings. Procedures - 4 horses remained sedentary, and 8 horses were exercised for 4 weeks at low intensity and 4 weeks at higher intensity, followed by 2 weeks of detraining. Prior to and after each training period, frequently sampled IV glucose tolerance tests with minimal model analysis were performed and baseline plasma insulin, glucose, triglycerides, non-esterified fatty acids, and leptin concentrations were analyzed. Adiposity was assessed by use of morphometrics, ultrasonic subcutaneous fat thickness, and estimation of fat mass from total body water (deuterium dilution method). Results - Body weight and fat mass decreased by 4% (mean ± SD, 20 ± 8 kg) and 34% (32 ± 9 kg), respectively, compared with pre-exercise values, with similar losses during low- and higher-intensity training. There was no effect of exercise training on subcutaneous fat thickness, plasma hormone and lipid concentrations, or minimal model parameters of glucose and insulin dynamics. Conclusions and Clinical Relevance - Results suggested that moderate exercise training without concurrent dietary restriction does not mitigate insulin resistance in overweight or obese horses. A more pronounced reduction in adiposity or higher volume or intensity of exercise may be necessary for improvement in insulin sensitivity in such horses.