© Laura Grubb with Albert J. Kane, DVM, MPVM
reprinted in ANVIL Magazine April 1997 from the Owners' Circle, Thoroughbred Owners of California
Flat, outer and inner rim shoe. |
Low, regular and high toe grabs. |
Bone, tendon and ligament injuries account for approximately 80% of the fatalities occurring on California Thoroughbred racetracks. In addition to causing owners economic and emotional hardship, these injuries threaten the safety of horses and jockeys alike, and present racing in a negative light to both members of the media and the racing fans. Although they are rare occurrences, catastrophic injuries do threaten the future of the California racing industry.
Some traction devices, particularly toe grabs, have been implicated as a cause of racehorse injury and lameness for many years. In an effort to understand why catastrophic injuries occur, a three-year study recently concluded by veterinarians at the U.C. Davis Veterinary Orthopedic Research Laboratory found an association between toe grabs and increased risk of fatal injury, particularly suspensory apparatus failure, for California Thoroughbreds.
Methodology of the study
Shod hooves were collected from 201 horses submitted to the California Veterinary Diagnostic Laboratory System (CVDLS) through the CHRB Postmortem Program. The presence of toe grabs, rims or flat shoes was recorded for all four limbs of each horse in the study. If present, the height of the toe grabs was recorded as low, regular or high; which are 4, 6 or 8mm tall when new. The age and gender of each horse was recorded as well as details of the cause of injury or death. All fatal injuries were studied as a group as well as the most common type of injury, suspensory apparatus failure.
Horses that died for reasons unrelated to the musculoskeletal system (e.g., colic, pneumonia) were used as controls for comparison to the injured horses. The potential increase or decrease in odds of injury associated with toe grabs or rims was determined by comparing the shoes of injured horses to those of the control horses. In addition, the influence of age and gender on the results was considered in the data analysis.
Results
With low toe grabs the odds of any injury and suspensory apparatus failure were 2 and 7 times greater, respectively, than those of horses shod without toe grabs. The odds of injury for horses shod with regular toe grabs were 3.5 times greater for any injury and 16 times greater for suspensory apparatus failure. These results clearly show that horses shod with toe grabs are more likely to be injured, and that the risk of injury increases with taller toe grabs. Because very few Thoroughbreds were shod with high toe grabs, estimates could not be made for their proportionate increase in odds of injury; however, it is likely that they would be even greater. The good news is with rim shoes, an alternative to toe grabs that still offer increased traction, the odds of injury were two-thirds lower compared to horses shod without rims.
How do toe grabs lead to these injuries?
"Because toe grabs only elevate the toe of the hoof, they lower the functional hoof angle (similar to the long toe/low heel conformation many racehorses develop) which may affect the angles of the joints up the limb while the horse is galloping," says Dr. Kane. "They may also give too much traction, stopping the hoof suddenly on each stride." He goes on to explain, "Each time a horse's hoof lands it naturally slides a little bit as it touches the ground. This helps dissipate some of the force of landing. With toe grabs we think the hoof may stop too quickly and additional forces may be transferred to the bones, tendons and ligaments, causing injury." He is quick to add, "The study we've just completed identified a link between grabs and injury, pointing us in the right direction. Exactly how they cause the injuries needs further research to examine these two theories. We would also like to look at more common injuries (e.g., bucked shins, strained suspensories) to see if a similar pattern exists with toe grabs and rims."
The University of California Davis research team hopes that by spreading the word among owners, trainers, farriers and veterinarians about the risk associated with toe grabs and the safer rim shoe alternative, they can decrease the risk of injury for horses and improve the safety of racing. This research was supported by the Grayson-Jockey Club Research Foundation, the California Center for Equine Health and Performance (formerly the Equine Research Laboratory) with funds provided by the Oak Tree Racing Association, the State of California satellite wagering fund, Mr. and Mrs. Amory J. Cooke, the Hearst Foundation, and by contributions of private donors.
References from the original study
Estberg, L, Stover SM, Gardner IA, et al. Descriptive study of fatal musculoskeletal injuries of Thoroughbred racehorses while racing and race training. JAVMA, 1996: 208:92-96. Johnson BJ, Ardans AA, Stover SM, et al. California Racehorse Post Mortem Program. Proceedings, AAEP, 1994: 40:167-169.
Kane AJ, Stover SM, Gardner IA, et al. Horseshoe characteristics as possible risk factors for fatal musculoskeletal injury of Thoroughbred racehorses. AJVR, 1996; 57: 1147-1152.
Kane AJ, Stover SM, Gardner IA, et al. Post-mortem evaluation of Thoroughbred racehorses, AJVR, 1996: 57:1141-1146. homotypic variation in horseshoe characteristics of 201
Moyer W, Anderson JP. Lameness caused by improper shoeing. JAVMA, 1975: 166:47-52.
Nack W, Musson L. The Breaking Point. Sports Illustrated, 1993: 79:76-90.
Pool RR, Meagher DM. Pathological findings and pathogenesis of racetrack injuries. Vet Clin North Am Equine Pract, 1990: 6:1-30. Rothman KJ. Modern Epidemiology. Boston: Little, Brown & Co., 1986:73-74.
Thompson KN, Herring LS. Hoof caulks and their influence on equine joint kinematics. Abstracts, 2nd Internatl Workshop Animal Locomotion, Assn Equine Sports Med; Fallbrook, CA, 1993: 56.
Wacholder S, Silverman DT, McLaughlin JK, Mandel JS. Selection of controls in case-control studies. Am J Epidemiology, 1992: 135:1029-1041.
Albert J. Kane, DVM, MPVM is a PhD candidate with the University of California Davis School of Veterinary Medicine's Veterinary Orthopedic Research Laboratory and the Department of Medicine and Epidemiology.
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