Competitive endurance riding challenges a horse’s athletic ability, stamina, and conditioning over rugged routes ranging from 50 to 100 miles. Because of the sport’s strenuous nature, endurance horses are at risk for colic due to dehydration, fatigue, and metabolic disorders.
Colic prevention, early intervention, and proper management during competition can mean the difference between life and death for endurance horses, said Yvette Nout-Lomas, DVM, PhD, Dipl. ACVIM, ACECC, assistant professor of equine internal medicine at Colorado State University’s Veterinary Teaching Hospital.
Nout-Lomas presented the paper “How to Treat Endurance Sport Horses With Colic at Competitions” at the 2017 American Association of Equine Practitioners Convention, held Nov. 17-21 in San Antonio, Texas. American Endurance Ride Conference (AERC, the U.S. governing body for endurance) veterinary chair Jeanette Mero, DVM, of Mariposa Equine Services, in California, co-authored the study, in which they reviewed AERC data, including recorded equine fatalities related to endurance competition.
During endurance rides, mandatory veterinary inspections take place between ride phases (about every 15 miles) to ensure horses can continue safely down the trail. At these inspections, veterinary officials evaluate horses’ heart rates, dehydration status, presence of gut sounds, and gait. Elimination is most commonly related to lameness, dehydration, and metabolic issues, Nout-Lomas said.
The researchers found that of eliminated horses, 12% required emergency veterinary treatment. Most of these horses requiring emergency intervention suffered from exertional rhabdomyolysis (a painful disorder that involves muscle breakdown due to overexertion) and colic. The AERC data indicate that ileus (slowed intestinal motility) and enteritis (inflammation of the small intestine) are the two most common causes of fatal colic in endurance horses.
The AERC data also indicated that the endurance horse fatality rate from 2002 to 2016 was 0.026%, which Nout-Lomas noted is lower than most other horse sports. “For example, The Jockey Club reports a fatality rate of 0.2%” in racing starts,” she said.
Still, Nout-Lomas and Mero saw a need for veterinarians to better understand how to treat endurance horses suffering from colic to improve outcomes.
“Our findings prompted the need to disseminate more information pertaining to colic in endurance horses to equine practitioners,” Nout-Lomas said.
For example, she said, most horses experiencing colic usually have elevated heart rates (sometimes over 100 beats per minute) indicative of their high pain levels. However, endurance horses usually have superior fitness and/or have naturally low heart rates, so even those with severe colic might not exhibit abnormally high heart rates. “Heart rates of 50 to 65 beats per minute (during a colic episode) are common,” Nout-Lomas said.
Additionally, Arabians are the most prevalent breed in endurance, and researchers have shown the breed is more susceptible to rectal tears than other horses. Dehydration might also increase risk of rectal tears. Because these two risks combine in Arabian or part-Arabian endurance athletes, the researchers recommended avoiding rectal examination when conducting initial colic evaluations in these horses.
To address dehydration veterinarians should fluid resuscitate horses early and aggressively with a balanced electrolyte solution delivered intravenously, Nout-Lomas said. Clinical signs of dehydration could include a persistently elevated heart rate (more than 60 beats per minute 20 minutes or more after stopping exercise) and anorexia (disinterest in feed), she said, noting that “horses with evidence of gastrointestinal (GI) disease or suspected to have GI disease should not be administered intragastric fluids due to concern of stomach distention and possible fatal rupture.”
Endurance horses with evidence of GI disease are more likely to benefit from intravenous fluid administration, she noted.
Dehydration also makes horses susceptible to kidney damage related to non-steroidal anti-inflammatory drug administration. For that reason, Nout-Lomas recommended avoiding NSAIDs for pain management in colicky endurance horses until a veterinarian is confident the horse is rehydrated.