Returning after a lay-up and absence of recent starts are associated with complete humerus fractures in Thoroughbred racehorses in South Korea (2009-2022).

Returning to training or racing after a lay-up period, especially without recent race starts, significantly increases the risk of complete humerus fractures in Thoroughbred racehorses in South Korea. This study identifies key risk factors and suggests preventive measures to reduce such injuries.

Study Objective and Design

• The primary goal was to determine the risk factors associated with complete humerus fractures in South Korean Thoroughbred racehorses.
• A retrospective case-control study design was used, analyzing data from 2009 to 2022.
• The study included 131 horses diagnosed with complete humerus fractures after racetrack activity and 660 healthy control horses with at least one racetrack activity during the same period.
• Multivariable logistic regression was employed to identify statistically significant risk factors.

Key Findings – Risk Factors for Humerus Fractures

• Recent return after a lay-up: Horses that resumed training within 20 days after a lay-up longer than 60 days were at a significantly higher risk of fractures (Odds Ratio [OR] 13.5; 95% Confidence Interval [CI]: 5.5–33.1).
• No recent race starts: Horses without any race starts in the 60 days before the fracture event had elevated risk (OR 11.6; 95% CI: 5.5–24.6).
• Activity type: Fractures were more likely during races or trials compared to routine racetrack training (OR 8.9; 95% CI: 4.3–18.7).
• Number of prior starts: Horses with only 1 to 5 previous starts had higher fracture risk (OR 4.8; 95% CI: 2.0–11.3), suggesting less experience or conditioning plays a role.
• Sex: Female horses and intact males showed increased susceptibility compared to other groups.
• Lack of previous trial race experience: Horses that had not participated in trial races before were at greater risk.
• Prolonged lay-up history: Horses with lay-ups exceeding 180 days also faced a higher risk.

Implications of the Findings

• The study highlights that breaks from training or racing, particularly extended lay-ups, disrupt conditioning and increase fracture risk when horses return to high-intensity activities.
• Inexperience, indicated by fewer prior starts or lack of trials, also contributes to vulnerability in the humerus bone during racing stresses.
• Periods without racing activity may result in bone weakening, leading to a higher chance of catastrophic fractures during strenuous exercise.

Preventive Recommendations

• Implement risk profiling to identify horses at higher fracture risk based on their lay-up duration, recent activity level, and racing history.
• Increase veterinary scrutiny before resumption of training or racing, including pre-exercise veterinary examinations that utilize diagnostic imaging (e.g., radiographs or ultrasonography) to detect early signs of bone stress or vulnerability.
• Gradually ease horses back into training and racing after lay-ups to allow reconditioning of bone strength and reduce sudden mechanical stress.
• Consider conditioning protocols targeting horses with fewer prior starts or no trial experience to enhance bone robustness.

Conclusion

• This study provides evidence that careful management of Thoroughbred racehorses, especially those returning from extended breaks or with limited racing experience, is vital to reducing complete humerus fractures.
• Integrating preventive veterinary care with tailored training approaches may decrease the incidence of these serious injuries, improving horse welfare and racing safety in South Korea.