Long distance races pose particular risks for horses. These include mechanical problems (stresses to muscles, tendons, ligaments, and bones, all of which can cause lameness and predispose to injury), as well as metabolic problems (exhaustion, dehydration, over-heating, electrolyte loss, and body pH changes, which can cause metabolic disease). Outcomes for affected horses can include incapacitation, death, lameness of many types, metabolic diseases, heatstroke, colic (abdominal pain caused by gastrointestinal problems), exertional rhabdomyolysis (muscle break-down), synchronous diaphragmatic flutter (which causes breathing difficulties), and exhausted horse syndrome .
1. Frazier DL. (2000). Who speaks for the horse-the sport of endurance riding and equine welfare. J Amer Vet Med Assoc, 216(8), 1258-1260.