Articles

"It's About Glycogen"
Mike Watkins, Ph.D.
Dairy Manufacturers, Inc.

Glycogen, or body starch, is glucose stored in the liver and muscle. It supplies glucose when energy demands require. It is a readily available source of quick energy for muscles when extreme exertion is needed or during prolonged exercise. Only the glycogen in the liver can be mobilized into the blood to provide energy for muscles and other tissue. Glycogen in muscle is used in the muscle tissue, where it resides and is needed. The energy in glycogen is about twice that of glucose circulating in the blood.

Blood glucose is used preferentially during the first few minutes of exercise; then free fatty acids become the primary energy source. Fats require carbohydrate (glucose) to be completely metabolized to energy, water and carbon dioxide. "Fats burn in the fire of carbohydrates"; therefore, glucose derived from glycogen is still needed. The virtual exhaustion of glycogen stores leads to fatigue. Dogs in better condition use glucose more efficiently and don’t fatigue as quickly as dogs of lesser condition. However, with enough work, all dogs get tired. The glycogen fuel tank is near empty.

The body begins replenishing glycogen stores following an exercise bout. Typical high-fat, high-protein dog foods contain about 45% carbohydrate, which usually comes from wheat flour, corn meal and/or rice. It is reported that dogs fed this type of diet require over 48 hours to replenish glycogen stores. Glycogen stores can be rebuilt faster by feeding a supplement composed of more readily available carbohydrates soon after the working bout.