Owners commonly report muscular fatigue of dogs and horses. Muscular fatigue can be caused by numerous disorders of several body systems, which are discussed in other chapters. Fatigue is an issue for working dogs, racing greyhounds, and dogs that compete in agility and other high-intensity events.

Fatigue is a normal consequence of exercise that is continued at high intensity or for prolonged periods of time. The decreased ability of the muscle to produce force is actually a safety mechanism for the body. If fatigue did not occur and force the animal to stop, the intense exercise could cause structural damage to muscle cells and supportive tissues.

During prolonged exercise (usually several hours or more), panting and/or sweating occur to remove excess heat generated by the body's metabolic processes. This leads to dehydration and acid-base and electrolyte imbalances. These factors cause fatigue, exhaustion, and may even lead to death.

Appropriate physical training is the most effective way to reduce fatigue and increase the capacity for exercise. Training leads to more effective use of oxygen in body tissues, increased blood volume, and muscle adaptations. Working animals should be acclimated to hot environments before competition.

If you have a working dog or one that competes in high-intensity events, you should consult with your veterinarian about appropriate feeding and hydration strategies to help minimize fatigue.

Last full review/revision July 2011 by George M. Barrington, DVM, PhD, DACVIM; Sharon J. Spier, DVM, PhD, DACVIM; Ivan W. Caple, BVSc, PhD, MACVSc, MRCVS; David L. Evans, BVSc, PhD; Jean A. Hall, DVM, PhD, DACVIM; Katharine F. Lunn, BVMS, MS, PhD, MRCVS, DACVIM; Donald C. Sawyer, DVM, PhD