Carbohydrate supplementation of horses during endurance exercise: Comparison of fructose and glucose

To delay the onset of fatigue, endurance horses are often fed at rest stops during races. The resulting increase in blood insulin may adversely inhibi t lipolysis. in humans, ingestion of fructose produces a smaller insulin ri se than glucose. This study compared glucose acid fructose as carbohydrate supplements for endurance horses. Three Arabian geldings were given 300 g o f fructose (F), glucose (G) or 50% glucose: 50% fructose (GF), in 1.5 L wat er, by stomach tube. In the Resting Test, carbohydrate was administered at rest. Following treatment, blood samples were taken every 30 min for 8 h, a nd feces were collected for 24 h. Treatment did not affect fecal weight or water content. Plasma glucose and insulin responses did not differ among tr eatments. Post-treatment (60 min), plasma L-lactate tended to be higher (P = 0.06) after the F and GF treatments than after the G treatment. In the Ex ercise Test, two treadmill exercise bouts at 0 degrees incline (Bout 1: 90 min; Bout 2: 120 min) were separated by a 1-h rest period. A total distance of 36.84 km was covered at a mean speed of 2.9 m/s. Carbohydrate was admin istered 45 min before Bout 2. Plasma glucose and insulin at the start of Bo ut 2 were higher (P = 0.02 and 0.03, respectively) with the GF treatment th an with the F treatment. However, during exercise, plasma glucose concentra tions did not differ among treatments. We conclude that fructose is well-ab sorbed by horses and rapidly converted to glucose.