Neuromuscular diseases, which affect the function of muscles and the way they interact with the nervous system, can lead to performance issues, said Kelsey A. Hart, DVM, PhD, Dipl. ACVIM, internal medicine clinician and graduate fellow at the University of Georgia's department of large animal medicine, at the recent American Veterinary Medical Association meeting in Atlanta, Ga.

The problem can be subtle. "The horse is just reluctant to work or quits while working," said Hart. "Or, you might have a horse that is truly lame or is generally stiff, but the owner cannot pinpoint the (cause for the) lameness."

The most common equine muscle disorder that affects performance is exertional rhabdomyolysis (tying-up, ER). Whether the problem ends the horse's career depends on the type of ER he has