Comparison of ventilatory and oxygen consumption measurements of yearling Thoroughbred colts and fillies exercising unridden on an all-weather track.
Authors: Katz L M, Gough K, McGivney C L, McGivney B, Sides R H, Hill E W, Bayly W M
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary Researchers from University College Dublin and UC Davis investigated whether sex differences in cardiorespiratory responses to exercise, well-documented in humans, also exist in young Thoroughbreds. Forty-one untrained yearlings (16 colts, 25 fillies) were exercised at high intensity on an all-weather track whilst wearing portable ergospirometry equipment and GPS-heart rate monitors to measure oxygen consumption and ventilatory parameters. Although colts and fillies showed no differences in absolute peak oxygen consumption, fillies demonstrated significantly higher mass-specific peak VO₂ (121.5 versus 111.9 mL/kg·min). The more interesting findings emerged in ventilatory mechanics: fillies exhibited greater peak breathing frequency, whilst colts demonstrated higher peak inspiratory and expiratory air flows, peak expiratory tidal volumes, and minute ventilation—differences that disappeared when adjusted for bodyweight. The authors attribute these patterns to morphological differences between sexes, hypothesising that smaller lung volumes and airway diameters in fillies create greater respiratory resistance, necessitating compensatory increases in breathing frequency. For practitioners, these findings suggest that sex-related differences in ventilatory efficiency may become increasingly important during athletic development and warrant consideration when evaluating respiratory performance or managing respiratory health in young stock. However, the authors emphasise that longitudinal research tracking these parameters through maturation is essential before drawing firm conclusions about performance implications or training recommendations.
Read the full abstract on PubMed
Practical Takeaways
- •Sex-based physiological differences in yearling Thoroughbreds may influence exercise capacity assessment and training protocols, with fillies demonstrating better mass-specific oxygen utilization
- •The greater breathing frequency but lower airflow volumes in fillies may reflect smaller lung volumes and airway diameters related to their smaller body size—monitor ventilatory response during training accordingly
- •Bodyweight normalization is essential when comparing physiological measurements between male and female yearlings, as absolute measurements may be misleading without accounting for size differences
Key Findings
- •Fillies had significantly higher mass-specific peak VO₂ than colts (121.5 vs 111.9 mL/kg·min, P=0.03) despite similar absolute peak VO₂
- •Peak breathing frequency was significantly greater in fillies (P<0.001), while peak inspiratory and expiratory airflow and peak minute ventilation were greater in colts (P<0.001 and P=0.01 respectively)
- •Bodyweight and wither height were significantly greater in colts than fillies (P=0.002 and P=0.04)
- •When adjusted for bodyweight, there were no differences in peak tidal volume or minute ventilation between sexes, suggesting morphological differences explain ventilatory variations