Endurance rides covering distances from 40 to 160 kilometers in a 24-hour period are grueling tasks for both horse and rider. So it’s not surprising to learn that up to 60% of horses can be eliminated for health reasons during the competition. A team of U.S. researchers recently set out to determine which factors, at the start and in the first or second half of rides, contribute to endurance horses’ elimination from competition.

"To our knowledge, this is the first study to look at a number of risk factors in a large group of horses over multiple rides to identify reasons that horses fail during competition," relayed lead author Langdon Fielding, DVM, Dipl. ACVECC, of Loomis Basin Equine Medical Center, in Loomis, Calif. "This data can help riders and veterinarians improve the completion rate and perhaps even prevent illness and injuries."

Fielding and colleagues collected rider cards (which contain detailed information about the animal) from 3,493 horses and collaborating veterinary information regarding the physical examinations during 2007 American Endurance Ride Conference sanctioned rides.

The researchers found that:

  • The overall elimination rate was 18.9% (660 of 3,493 horses);
  • The most common reasons for elimination were lameness (312/660) and metabolic problems (147/660); metabolic causes include poor heart rate recovery, colic, exhaustion, synchronous diaphragmatic flutter (thumps), and exertional rhabdomyolysis (tying-up);
  • Appaloosas, Quarter Horses, and other breeds with higher body mass index (compared to Arabians, one of the most common breeds in endurance compe