Alternative nutritional strategies for enhancing glycogen resynthesis in horses

Recovery of skeletal muscle glycogen is very slow in horses compared to other mammals studied, and can take 48--72 h, even when a highly soluble carbohydrate meal is fed immediately after exercise. There is a clear need to develop a practical nutritional strategy to enhancing recovery of muscle glycogen in horses. The studies described herein were intended to characterize the effects of supplemental acetate and effective rehydration on plasma and skeletal muscle in horses, in order to determine if the slow rate of muscle glycogen resythesis after glycogen-depleting exercise is due to a combination of slow recovery of hydration and inadequate shuttling of intracellular glucose towards glycogenesis. In two separate research studies gluteus medius biopsies and jugular venous blood was sampled from exercise conditioned horses on 2 separate occasions, at rest and for 24 h following a competitive exercise test (CET) designed to simulate the speed and endurance test of a 3-day event and induve significant glycogen and total body water losses. In the first study, following the CETs horses were given either water ad libitum and either a hypotonic commercial electrolyte solution via nasogastric tube followed by a typical hay/grain meal, or a hay/grain meal alone. Electrolyte supplementation resulted in an enhanced rate of muscle glycogen resynthesis and faster restoration of hydration, as evidenced by faster recovery of plasma [protein], maintenance of plasma osmolality and greater muscle intracellular fluid volume during the recovery period compared to control. In the second study, following the CETs horses were allowed water ad libitum and either a sodium acetate/acetic acid solution via nasogastric tube followed by a typical hay/grain meal, or a hay/grain meal alone. Acetate supplementation resulted in a rapid and sustained increase in plasma [acetate], and increases inkeletal muscle [acetyl-CoA] and [acetylcarnitine]. Acetate supplementation also resulted in an enhanced rate muscle glycogen resynthesis during the initial 4 h of the recovery period compared to control. It is concluded that both electrolyte and acetate supplementation can be used to enhance glycogen resynthesis in athletic horses.