Gender differences in bone turnover in 2-year-old Thoroughbreds.
Authors: Jackson B F, Lonnell C, Verheyen K, Wood J L N, Pfeiffert D U, Price J S
Journal: Equine veterinary journal
Summary
# Editorial Summary: Gender Differences in Bone Turnover in 2-Year-Old Thoroughbreds During a ten-month monitoring period, Jackson and colleagues measured three biochemical markers of bone metabolism in 84 colts and 63 fillies in race training, all aged approximately 20 months, to investigate whether sex-based differences in skeletal injury risk reflect underlying differences in bone cell activity. Colts demonstrated significantly higher osteocalcin concentrations (indicating greater bone formation; 3.62 ng/ml higher, P = 0.044) and elevated ICTP levels (bone resorption marker; 0.68 mg/l higher, P = 0.01) compared to fillies, suggesting a more active bone turnover phenotype in males—though the less bone-specific marker PICP showed no overall gender effect, with an interesting exception in May when fillies' PICP concentrations spiked 157 mg/l above colts' levels. These findings suggest that fillies may have smaller skeletal dimensions and achieve skeletal maturity earlier than colts, whilst the seasonal elevation in collagen turnover markers in fillies during spring indicates sex hormone influence on bone physiology. For practitioners managing young Thoroughbreds in training, these differences in bone remodelling capacity merit consideration when individualising training progression, monitoring injury risk, and interpreting diagnostic bone imaging between sexes, as colts' elevated bone turnover may enhance adaptive capacity to training stress whilst simultaneously creating different injury vulnerability profiles compared to fillies.
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Practical Takeaways
- •Colts and fillies have inherently different bone turnover rates at 2 years old; fillies may have smaller bone size and/or earlier skeletal maturation, which could affect training load tolerance differently between genders
- •The seasonal spike in collagen turnover (PICP) in fillies during spring/early summer suggests sex hormones influence bone metabolism and may warrant gender-specific management during this period
- •These physiological differences may partially explain why gender influences injury risk in young racehorses and should inform individualized conditioning programs rather than uniform protocols
Key Findings
- •Colts had significantly higher osteocalcin concentrations (3.62 ng/ml higher, P=0.044) and ICTP concentrations (0.68 mg/l higher, P=0.01) than fillies
- •Fillies showed 157 mg/l higher PICP concentrations in May compared to colts, suggesting sex hormone influence on collagen turnover
- •Age and season had no statistically significant effect on bone turnover markers within the 18-23 month age range studied
- •Gender differences in bone cell activity may influence adaptive responses to training and injury risk in 2-year-old Thoroughbreds