Gelded racehorses are three times more likely than race mares to damage their superficial digital flexor tendon, a Japanese study has found.
Injuries to this crucial tendon in the lower leg of racehorses is common.
Orthopaedic diseases are responsible for retirement in 76% of racehorses, of which nearly half are because of superficial digital flexor tendinopathy.
Injuries to this crucial tendon can arise through microdamage through ageing and training load.
Superficial digital flexor tendinopathy develops in 6% to 13% of racehorses during racing. It affects 6% of 2-year-old racehorses, 20% of 3-year-olds, 17% of 4-year-olds and 12% of those aged 5 and older. Its average prevalence is 14%.
Yoko Ikeda and her colleagues set out to learn more about the risk factors for injuries to this tendon in Thoroughbred racehorses in Japan.
The Azabu University study focused on 292 racehorses with superficial digital flexor tendinopathy based on racetrack medical records from Oi Racecourse. All horses had been diagnosed based on ultrasonography.
Two unaffected control horses were matched to each case horse for the study, reported in the Journal of Equine Science, published by the Japanese Society of Equine Science.
Looking at track variables, the researchers found that the odds of developing an injury to the tendon were significantly higher for a sloppy track surface compared with a standard track surface.
Looking at race variables, the odds of an injury to the tendon was significantly higher in horses finishing in 10th place or worse. The odds of an injury were also higher in races under 1300m, which the authors put down to increased microdamage as a consequence of multiple concussion force experienced during the races due to the increased speed.
Horses at the worst odds — placed eighth or lower in the field in terms of betting, were at 1.49 times the risk of an injury to the tendon.
Turning to horse-related factors, they found that the body weight of affected racehorses was significantly heavier than that of control horses. When body weight at race time was 470kg or more, the horse was 1.55 times more likely to injure the tendon.
They also found that, when there was a decrease in body weight since previous racing of 5kg or more, the odds of an injury to the tendon rose. The authors noted that decreased body weight might not only be the result of muscle loss or excessive training, but also be the result of intentional weight reduction in training to improve race performance.
Geldings were 3.09 times were more likely to suffer an injury to the tendon than race mares, and stallions were 1.35 times more likely than mares. This, they said, indicated that the slower gait speed of female horses could potentially reduce tendon strain.
“As a countermeasure to prevent superficial digital flexor tendinopathy, sloppy track surfaces should be avoided during races by guiding horses toward more solid track surfaces,” the study team wrote.
“Short distance with faster races should be avoided, if possible, and selecting long distance with slower speed races could lower the risk …”
They said further investigations with larger sample sizes were warranted to clarify the positive or negative impact of decreases in body weight and the length of the race interval on the risk of injury to the tendon.
The study team comprised Ikeda, Akikazu Ishihara and Kazutaka Yamada, all with Azabu University; and Masahiko Nakajima, with the Tokyo Metropolitan Racing Association.
Risk factors for superficial digital flexor tendinopathy in Thoroughbred racing horses in Japan
Yoko Ikeda, Akikazu Ishihara, Masahiko Nakajima and Kazutaka Yamada.
J Equine Sci. 2019; 30(4): 93–98. Published online 2019 Dec 18. doi: 10.1294/jes.30.93