Effects of Standardized Exercise Tests on Plasma Thyroid Hormones' Kinetics in Standardbred Racehorses.
Authors: Fazio Esterina, Lindner Arno, Cravana Cristina, Wegener Julia, Medica Pietro, Hart-Mann Ulrich, Ferlazzo Adriana
Journal: Journal of equine veterinary science
Summary
# Editorial Summary: Thyroid Hormone Responses to Exercise in Standardbred Racehorses Thyroid hormones influence metabolic rate and exercise capacity, yet their response to standardised exertion in racing horses remains poorly characterised. Researchers subjected twelve trained Standardbred racehorses (across three age groups: 2, 3, and 4 years old, split evenly by sex) to standardised exercise tests designed to reach blood lactate thresholds of 4 mmol/L, collecting blood samples at rest and throughout exercise to measure total and free triiodothyronine (T3, fT3) and thyroxine (T4, fT4). Both T3 and fT3 increased significantly during exercise, with concentrations notably higher in 4-year-olds compared to younger cohorts, and substantially elevated in mares relative to stallions across all age groups. Critically, higher velocity at lactate 4 (VLa4)—an established marker of aerobic fitness—correlated inversely with thyroid hormone responses, though this relationship was significant only in 2-year-old mares, suggesting that sex and age substantially modulate the hormonal adaptation to training stress. These findings indicate that thyroid hormone kinetics during exercise testing could potentially serve as a supplementary performance biomarker in Standardbred racehorses, particularly for assessing training adaptation and recovery status in age and sex-stratified cohorts, though additional research is needed to establish clinical thresholds and predictive value for practitioners managing racing stock.
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Practical Takeaways
- •Thyroid hormone responses to standardized exercise tests vary significantly by age and sex in Standardbred racehorses, suggesting these factors should be considered when using hormonal data for performance evaluation
- •The inverse relationship between VLa4 and thyroid responses in young mares may provide additional insight into training adaptation and fitness status, though further research is needed before implementing this clinically
- •Sex-specific and age-specific reference ranges for thyroid hormones during exercise may be necessary for accurate interpretation of thyroid function in racing populations
Key Findings
- •Standardized exercise tests significantly increased plasma T3 and fT3 concentrations in trained Standardbred racehorses
- •4-year-old horses demonstrated higher plasma T3 and fT3 concentrations compared to 2 and 3-year-old groups
- •Mares had higher all plasma thyroid hormone concentrations than stallions across all age groups
- •In 2-year-old mares, higher VLa4 (velocity at 4 mmol/L lactate) was inversely correlated with thyroid hormone responses to exercise