Born to run? Associations between gestational and early‐life exposures and later‐life performance outcomes in Thoroughbreds

Background Gestational and early‐life exposures may modulate development during growth and influence future athletic performance. Objectives To investigate associations between gestational and early‐life exposures in Thoroughbreds and (i) likelihood of racing, (ii) total number of runs and (iii) total prizemoney by the end of the 3‐year‐old year. Study Design Prospective cohort. Methods Daily records were kept on the location and duration of turnout, management and veterinary‐attended episodes of disease or injury from birth until leaving the farm or study exit for 129 Thoroughbred foals on six stud farms. Dams' signalments, reproductive and gestational health records were collated concurrently. Available race performance records to the end of the fourth year of life were collected from industry databases. Mixed effects logistic and linear regression modelling, including farm, mare and stallion as random effects, were used to investigate associations between gestational and early‐life exposures and race performance outcomes. Results Overall, 76% (98/129, 95% CI: 68–82) of horses raced, making a median of 7 starts (IQR 4–11, range 1–23) and earning a median of £6898 (IQR 1712–17,987; range 0–197,601) in prizemoney. Increasing average daily turnout time (hours) and turnout area (acres) in the first 6 months of life were associated with increased odds of racing and increased total prizemoney earned, respectively (OR 1.31, 95% CI: 1.09–1.58 p = 0.004 and β ‐coefficient = 0.32 (lnGBP), 95% CI: 0.03–0.61, p = 0.03). Age at weaning (days) was associated with increased odds of racing and an increased total number of runs (OR 1.03, 95% CI: 1.01–1.05 and β ‐coefficient = 0.09, 95% CI: 0.04–0.14, p < 0.05, respectively). Main Limitations Absence of training‐related data; low study power for some exposure variables. Conclusions More extensive early‐life turn out practices and later weaning enhanced later‐life race performance outcomes. This could be due to increased opportunity for positive musculoskeletal tissue adaptation and optimal growth and development rates during a critical window of developmental plasticity.