Glycemic index of a meal fed before exercise alters substrate use and glucose flux in exercising horses

1 Department of Veterinary Clinical Sciences, College of Veterinary Medicine and 2 Section of Sport and Exercise Sciences, The Ohio State University, Columbus 43210; and 3 Department of Health and Sport Science, School of Education and Allied Professions, University of Dayton, Dayton, Ohio 45469 In a randomized, balanced, crossover study each of six fit, adult horses ran on a treadmill at 50% of maximal rate of oxygen consumption for 60 min after being denied access to food for 18 h and then 1 ) fed corn (51.4 kJ/kg digestible energy), or 2 ) fed an isocaloric amount of alfalfa 2-3 h before exercise, or 3 ) not fed before exercise. Feeding corn, compared with fasting, resulted in higher plasma glucose and serum insulin and lower serum nonesterified fatty acid concentrations before exercise ( P