Obesity is of increasing concern in equid populations because its presence is associated with altered metabolic function and risk for disease. Obesity has been associated with insulin resistance in horses and ponies,1–3 and obesity and insulin resistance have been associated with impaired reproductive function in mares and an increased risk of and a predisposition for developing pasture-associated laminitis.4–7 In addition to insulin resistance, other obesity-associated factors have been implicated in increasing risk for pasture-associated laminitis, including hyperinsulinemia and hyperleptinemia.8 Therefore, developing management strategies that mitigate the extent of obesity and insulin resistance is important for lessening disease risk in obese horses.
In humans, regular exercise is recommended for weight reduction and management of metabolic disease,9 and research has helped to elucidate the amount and intensity of exercise necessary for desired effects.10,11 Studies in humans and rodents suggest that improvements in SI with exercise training may be induced by increased glucose transporter 4 content in skeletal muscle and increased expression or activity of proteins involved in signal transduction, including insulin receptor substrate 1 and phosphatidylinositol 3-kinase.12 Additionally, exercise training in obese subjects may improve SI through mechanisms involving weight reduction.13
Previous studies14,15 in horses support a role of short-term (7-day) exercise training for increasing SI, although sustained effects lasting > 1 day after the last exercise session are inconsistent. Additionally, in obese, insulin-resistant ponies, decreased adiposity through controlled feed intake increases SI to a similar degree as exercise training alone.16 However, it is unknown whether longer-term exercise training without feed restriction would induce a sustained increase in SI or reduction in adiposity in obese, insulin-resistant horses. It is also of interest to determine whether alterations in obesity and metabolism are dependent on intensity level of exercise training.
The present study was designed to test the hypothesis that exercise training in overweight or obese, insulin-resistant horses mitigates risk factors for metabolic disease and laminitis, that high-intensity exercise is more effective at altering these risk factors, and that these alterations will be present up to 2 weeks after the cessation of exercise training. The specific objectives of this study were to identify changes in measurements of adiposity, minimal model parameters of glucose and insulin dynamics, and circulating concentrations of insulin, glucose, NEFAs, triglycerides, and leptin in obese, insulin-resistant horses in response to low-intensity and higher-intensity exercise training without dietary restriction, and to determine whether these changes persist for a 2-week sedentary detraining period.
Acute insulin response to glucose
Body condition score
Frequently sampled IV glucose tolerance test
Nonesterified fatty acid
Total body water
Odyssey Horse Exerciser, Odyssey Performance Ltd, Rockwood, ON, Canada.
Equi Gym Products LLC, Paris, Ky.
Polar Pacer, Polar CIC Inc, Port Washington, NY.
Cambridge Isotope Laboratories Inc, Andover, Mass.
Dextrose 50% solution, Vedco Inc, St Joseph, Mo.
Humulin R, Eli Lilly & Co, Indianapolis, Ind.
CX5 Chemistry Analyzer, Beckman Coulter Inc, Fullerton, Calif.
Coat-A-Count Insulin, Diagnostic Products Corp, Los Angeles, Calif.
Multi-species Leptin RIA, Linco Research Inc, St Charles, Mo.
Metabolic Solutions Inc, Nashua, NH.
MinMod Millenium, version 5.15, Raymond Boston, University of Pennsylvania, Kennett Square, Pa.
Intercooled Stata, version 9.2, Stata Corp, College Station, Tex.
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