Route of carbohydrate administration affects early post exercise muscle glycogen storage in horses

Effect of Exercise Conditioning on Countering the Effects of Obesity and Insulin Resistance in Horses-A Review

Obesity is an important health concern in horses, along with humans and companion animals. Adipose tissue is an inflammatory organ that alters the insulin-signaling cascade, ultimately causing insulin dysregulation and impaired glucose metabolism. These disruptions can increase the risk of metabolic disease and laminitis in horses and may also impact energy metabolism during exercise. A single bout of exercise, along with chronic exercise conditioning, increases insulin sensitivity and glucose disposal via both contraction- and insulin-mediated glucose uptake pathways. Regular exercise also increases calorie expenditure, which can facilitate weight (as body fat) loss. This paper explores the metabolic pathways affected by adiposity, as well as discusses the impact of exercise on insulin metabolism in horses.

Nutritional Influences on Skeletal Muscle and Muscular Disease

Skeletal muscle comprises 40% to 55% of mature body weight in horses, and its mass is determined largely by rates of muscle protein synthesis. In order to support exercise, appropriate energy sources are essential: glucose can support both anaerobic and aerobic exercise, whereas fat can only be metabolized aerobically. Following exercise, ingestion of nonfiber carbohydrates and protein can aid muscle growth and recovery. Muscle glycogen replenishment is slow in horses, regardless of dietary interventions. Several heritable muscle disorders, including type 1 and 2 polysaccharide storage myopathy and recurrent exertional rhabdomyolysis, can be managed in part by restricting dietary nonstructural carbohydrate intake.

Nutritional aspects of post exercise skeletal muscle glycogen synthesis in horses: a comparative review

Carbohydrate (CHO) stored in the form of skeletal muscle glycogen is the main energy source for glycolytic and oxidative ATP production during vigorous exercise in mammals. In man, horse and dog both short-term high intensity and prolonged submaximal exercise deplete muscle glycogen. In horses, however, muscle glycogen synthesis is 2-3-fold slower than in man and rat, even when a diet high in soluble CHO is fed. There appear to be significant differences in CHO and glycogen metabolism between horses and other mammals, and it is becoming increasingly clear that many conclusions drawn from human exercise physiology do not apply to horses. This review aims to provide a comprehensive, comparative summary of the research on muscle glycogen synthesis in horse, man and rodent. Species differences in CHO uptake and utilisation are examined and the issues with feeding high soluble CHO diets to horses are discussed. Alternative feeding strategies, including protein and long and short chain fatty acid supplementation and the importance of rehydration, are explored.

Oral acetate supplementation after prolonged moderate intensity exercise enhances early muscle glycogen resynthesis in horses

Oral acetate supplementation enhances glycogen synthesis in some mammals. However, while acetate is a significant energy source for skeletal muscle at rest in horses, its effects on glycogen resynthesis are unknown. We hypothesized that administration of an oral sodium acetate-acetic acid solution with a typical grain and hay meal after glycogen-depleting exercise would result in a rapid appearance of acetate in blood with rapid uptake by skeletal muscle. It was further hypothesized that acetate taken up by muscle would be converted to acetyl CoA (and acetylcarnitine), which would be metabolized to CO2 and water via the tricarboxylic acid cycle, generating ATP within the mitochondria and thereby allowing glucose taken up by muscle to be preferentially incorporated into glycogen. Gluteus medius biopsies and jugular venous blood were sampled from nine exercise-conditioned horses on two separate occasions, at rest and for 24 h following a competition exercise test (CET) designed to simulate the speed and endurance test of a 3 day event. After the CETs, horses were allowed water ad libitum and either 8 l of a hypertonic sodium acetate-acetic acid solution via nasogastric gavage followed by a typical hay-grain meal (acetate treatment) or a hay-grain meal alone (control treatment). The CET significantly decreased muscle glycogen concentration by 21 and 17% in the acetate and control treatments, respectively. Acetate supplementation resulted in a rapid and sustained increase in plasma [acetate]. Skeletal muscle [acetyl CoA] and [acetylcarnitine] were increased at 4 h of recovery in the acetate treatment, suggesting substantial tissue extraction of the supplemented acetate. Acetate supplementation also resulted in an enhanced rate of muscle glycogen resynthesis during the initial 4 h of the recovery period compared with the control treatment; however, by 24 h of recovery there was no difference in glycogen replenishment between trials. It is concluded that oral acetate could be an alternative energy source in the horse.

Fluid and electrolyte supplementation after prolonged moderate-intensity exercise enhances muscle glycogen resynthesis in Standardbred horses

We hypothesized that postexercise rehydration using a hypotonic electrolyte solution will increase the rate of recovery of whole body hydration, and that this is associated with increased muscle glycogen and electrolyte recovery in horses. Gluteus medius biopsies and jugular venous blood were sampled from six exercise-conditioned Standardbreds on two 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. After the CETs, horses were given water ad libitum, and either a hypotonic commercial electrolyte solution (electrolyte) via nasogastric tube, followed by a typical hay/grain meal, or a hay/grain meal alone (control). The CET resulted in decreased total body water and muscle glycogen concentration of 8.4 ± 0.3 liters and 22.6%, respectively, in the control treatment, and 8.2 ± 0.4 liters and 21.9% in the electrolyte treatment. Electrolyte resulted in an enhanced rate of muscle glycogen resynthesis and faster restoration of hydration (as evidenced by faster recovery of plasma protein concentration, maintenance of plasma osmolality, and greater muscle intracellular fluid volume) during the recovery period compared with control. There were no differences in muscle Na, K, Cl, or Mg contents between the two treatments. It is concluded that oral administration of a hypotonic electrolyte solution after prolonged moderate-intensity exercise enhanced the rate of muscle glycogen resynthesis during the recovery period compared with control. It is speculated that postexercise dehydration may be one key contributor to the slow muscle glycogen replenishment in horses.