Factors associated with particularly high odds of musculoskeletal injury in Thoroughbred racehorses have been identified by Australian researchers.
University of Queensland researcher Kylie Crawford and her colleagues, writing in the journal Animals, said musculoskeletal injuries continue to affect Thoroughbred racehorses around the world, despite more than 30 years of research into the problem.
Many injuries and fatalities occurred during training rather than during racing, yet most studies report racing data only, they noted.
“There is a strong interest in developing training and management strategies to reduce their impact, however, studies of risk factors report inconsistent findings,” they said.
This meant the development of training strategies to reduce the risk was difficult.
By combining racing and training data, the true effect of risk factors may be more accurately represented, they said.
“Furthermore, modifications to reduce the impact of musculoskeletal injuries are more readily implemented at the training level.”
The study team set out to determine not only the risk factors for musculoskeletal injuries, but whether these are different for two-year-old and older horses. They also sought to determine whether risk factors varied with the type of injury.
The work focused on Thoroughbreds in training in south-east Queensland, with injury cases recruited from training stables, which were monitored weekly, over a 56-week period. Controls were recruited with every injury case added to the study.
Detailed training and exercise data were collected for both cases and controls through personal structured weekly interviews with participating trainers or their senior personnel.
In all, information on 202 cases and 202 matched controls were collected for analysis.
The study team identified four factors associated with particularly high odds of injury in this population of racehorses:
- Two-year-old Thoroughbred who were the first-born of mares were found to be at increased risk, particularly for shin soreness, which is more formally known as dorsal metacarpal disease;
- Two-year-old horses who had a total preparation length of between 10 and 14 weeks;
- Thoroughbreds of all ages that ran a total distance of 2.4 to 3.8km (12–19 furlongs) at a fast gallop (faster than 15 m/s; 13 s/furlong; 900 m/min; 55 km/h) in the four weeks preceding injury; and
- Horses three years and older that ran 3.0 to 4.8km (15–24 furlongs) at three-quarter pace and above (faster than 13 m/s; 15 s/furlong; 800 m/min; 48 km/h).
“We recommend that these horses should be monitored closely for impending signs of injury,” the study team said.
Increasing total preparation length was linked to higher odds of injury in horses of all ages, but particularly in two-year-old horses.
An increasing number of days exercised at a slow pace decreased the odds of injury in horses of all ages.
“This is consistent with other reports and our understanding of response to exercise, as the magnitude of the forces and strains generated during slow work are less likely to result in tissue failure than those forces experienced during high-speed exercise.
“Increasing the number of days worked at a slow pace may be more effective for preventing injury, if horses are perceived at a higher risk, than resting the horse altogether,” they said.
Increasing dam parity — that’s the number of births mares had — significantly reduced the odds of injury in horses of all age groups.
Discussing this finding, the researchers said dam parity is more likely to be associated with a risk of musculoskeletal injury in two-year-old horses rather than older horses because of the tissue development and adaptation occurring from training.
“It is plausible that increasing dam parity could decrease the odds of musculoskeletal injuries in two-year-old horses through increasing birthweight and, therefore, increasing volumetric bone mineral density.”
Seasoned broodmares are known to produce foals with heavier birth weight than those pregnant for the first time. “Heavier body weight is associated with a higher volumetric bone density in human children, although this information is not available for horses.”
The authors reported that there was a non-linear association between high-speed exercise and injury, whereby the odds of injury initially increased and subsequently decreased as accumulated high-speed exercise distance increased. This, they said, highlighted the importance of high-speed exercise to enable tissue adaptation to training.
None of the racing career and performance indices affected the odds of injury.
A long preparation time (a longer period in which the horse is remaining in race training without rest) was associated with increased odds of injury in two-year-olds, but not older, horses.
Two-year-old horses are likely more at risk of injury as total preparation length increases because they need the rest period to enable their tissues to repair and adapt to the effects of race training, the authors said.
“In contrast, tissue adaptation has already occurred in older horses and they can withstand longer periods in race training.”
The authors noted that the risk factors for injuries among two-year-old horses in the study were equivalent to those for older horses, with the exception of dam parity and the length of the training preparation.
“The maturity of a racehorse and the ideal starting time for training is strongly debated, with limited supporting literature.
They continued: “While the lack of significant findings supports the possibility that there is no long-term harm in racing horses at two years of age, it does not confirm that early exercise is beneficial either.
“Furthermore, there is the issue of survival bias, whereby those individuals that are injured early are removed and those remaining are at a reduced risk of injury.”
They said there is a need for prospective studies to evaluate whether starting horses at two years of age is associated with an increased or decreased risk of injury.
The study team said that early identification of horses at increased risk, and appropriate intervention, could substantially reduce the impact of musculoskeletal injuries in racehorses.
The study comprised Crawford, Anna Finnane, Solomon Woldeyohannes, Nigel Perkins, Lisa Kidd and Benjamin Ahern, all with the University of Queensland; Clive Phillips, with Curtin University in Perth; and Ristan Greer, with Torus Research in Queensland.
Crawford, K.L.; Finnane, A.; Phillips, C.J.C.; Greer, R.M.; Woldeyohannes, S.M.; Perkins, N.R.; Kidd, L.J.; Ahern, B.J. The Risk Factors for Musculoskeletal Injuries in Thoroughbred Racehorses in Queensland, Australia: How These Vary for Two-Year-Old and Older Horses and with Type of Injury. Animals 2021, 11, 270. https://doi.org/10.3390/ani11020270