The Horse

APR 2019

The Horse:Your Guide To Equine Health Care provides monthly equine health care information to horse owners, breeders, veterinarians, barn/farm managers, trainer/riding instructors, and others involved in the hands-on care of the horse.

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44 April 2019 The Horse | Rosanowski's team published a 2017 study 3 using the same data set that showed epistaxis incidence was 1.59 per 1,000 starts on all-weather surfaces. Faster (firmer) going increased a horse's odds of epistaxis and distal (lower) limb fracture but not fatality. Longer race distance increased the odds of fatality but reduced the odds of epistaxis. The odds of distal limb fracture increased with firmer surfaces, with more than 14 runners in a race, with increased horse age at first start, in better- performing horses, and in horses that raced eight to 93 days previ- ously. Horses from trainers with higher win percentages on all-weather surfaces were at increased odds of fracture, as well. Preventing Catastrophic Injuries Researchers at the University of California, Davis, (UC Davis) have been studying racehorses in various capacities, particularly their injury risk, for decades. "Because 80% of racehorse deaths are due to catastrophic injuries, focus on factors that affect injury risk should be a high priority," says Susan Stover, DVM, PhD, Dipl. ACVS, director of the UC Davis J.D. Wheat Veterinary Research Laboratory. "Because the causes of injury are multifactorial, a several-pronged approach is needed," including racing surfaces, hoof management and shoeing, and training schedules. She says her team's most recent impactful findings include using ul- trasound to detect humeral (the bone between the shoulder and elbow joints) stress fractures in racehorses (TheHorse. com/167901) and positron emission tomography (PET scan) to detect pre- existing issues that could lead to cata- strophic fetlock injuries. In a 2018 study 4 UC Davis researchers compared the use of PET scans with F- sodium fluoride (F-NaF, which serves as a tracer to detect changes in bone) to other methods of diagnosing bone-stress- related fetlock injuries, in hopes of preventing catastrophic injury. They found that PET scans with F-NaF picked up more bone lesions than nuclear scintigraphy (bone scan), computed tomography (CT), stand- ing magnetic resonance imaging (MRI), and histologic (microscopic) examination. They concluded that a combination of PET with CT is important for localizing these lesions because PET findings reflect the tissues' metabolic activity and CT pro- vides the activity's anatomic location. "Consequently, PET has particular advantages for imaging the fetlock in racehorses because of its usefulness for not only detecting but also discriminating between metacarpal condylar (the distal cannon bone) and proximal sesamoid (in the fetlock hinge joint) bone abnormali- ties," said the study authors. "California has made several changes to the industry that stemmed from UC Davis research and have contributed to an overall reduction in injuries in race- horses," says Stover. "The first key discov- ery was the recognition that catastrophic bone fractures were the acute manifesta- tion of more chronic (pre-existing) stress fractures." Because the fetlock is the most com- mon site of musculoskeletal injury in racehorses and the leading cause of fa- talities in the U.S., UC Davis researchers have focused on the relationship between race surface hardness and fetlock injury risk. This has led tracks to harrow (drag) racing surfaces more frequently during training sessions to help prevent injuries. Using computer simulations, UC Davis researchers also recently looked at race surfaces' effects on fetlock motion during the stride's stance phase (when the foot is in contact with the ground). 5 They found that, basically, providing sufficient cush- ion material on top of the surface's harder base can help prevent abnormal fetlock motion and reduce injury risk. The team concluded that harrowing depth and frequency can influence limb motion significantly. They said computer simulations can give researchers more in- formation on how race surface design and maintenance might reduce injury risk. Stover says future UC Davis studies will focus on sesamoid bone fracture causes in racehorses, hard arena surface effects on the extended trot in dressage horses, economical ways to detect humeral stress fractures using ultrasound, and arena surface property effects on show jumpers. Take-Home Message This is just a small sampling of the research involving racehorses around the world. As scientists reveal more informa- tion about and ways to preserve race- horse health, their findings can translate to athletic horses of all types. Some are even leading to follow-up studies involv- ing sport horses specifically. These studies might be "of even greater importance to the sport horse due to ... the fact that you're expecting years of performance out of that animal," says Horohov. "The ability … to both prevent as well as overcome injury is critical to the long-term health of that horse and the program it's involved in." h REFERENCES 1. Physick-Sheard PW, et al. (2019). Ontario Racehorse Death Registry, 2003-2015; Descriptive analysis and rates of mortality. Equine Veterinary Journal, 51:64-76. 2. Rosanowski SM, et al. (2018). Risk factors for a race- day fatality in flat racing Thoroughbreds in Great Britain (2000 to 2013). PLoS ONE 13(3): e0194299. 3. Rosanowski SM, et al. (2017). Risk factors for race-day fatality, distal limb fracture, and epistaxis in Thorough- bred racing on all-weather surfaces in Great Britain (2000 to 2013). Journal of Preventive Veterinary Medi- cine, 148:58-65. 4. Spriet M, et al. (2018). F-sodium fluoride positron emis- sion tomography of the racing Thoroughbred fetlock: Vali- dation and comparison with other imaging modalities in nine horses. Equine Veterinary Journal, 0:1-9. 5. Symons JE, et al. (2017). Modelling the effect of race surface and racehorse limb parameters on in silico fetlock motion and propensity for injury. Equine Veteri- nary Journal, 49:681-687. SPORTS MEDICINE ISTOCK.COM In one study British researchers found that all-weather racing surfaces increase fatality risk.

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