Comparison of ventilatory and oxygen consumption measurements of yearling Thoroughbred colts and fillies exercising unridden on an all-weather track.

The research aims to identify if there are differences in ventilatory and oxygen consumption behaviors during exercise between male and female young, untrained racehorses. The study indicates that while there are some differences between the sexes, these differences are primarily influenced by body weight and potentially, lung and airway size.

Introduction to the Research

• This study was undertaken to understand the ventilation and oxygen consumption measurements (V̇O) in exercising yearling Thoroughbreds (Tb) and whether these differ based on the sex of the horse. Previous research has shown sex effects in these parameters in humans.
• 41 Tb horses, 16 colts (males) and 25 fillies (females), with an approximate age of 19.8 months, were studied.
• Physiological, ventilation, and exercise data was collected while the horses exercised unridden at high intensity on an all-weather track.
• A global positioning-heart rate unit and a portable ergospirometry system were used to gather the data, which was then analysed with statistical tests.

Bodyweight and Wither Height Differences

• The research found significant differences in mean bodyweight and wither height (the height at the shoulder) between colts and fillies.
• Colts were found to have a greater bodyweight and wither height than fillies.

Ventilatory and Oxygen Consumption Differences

• No differences were found in absolute peak V̇O between colts and fillies.
• However, fillies exhibited a higher mass-specific peak V̇O – the amount of oxygen used per kilogram of bodyweight – than colts.
• Furthermore, fillies also had a greater peak breathing frequency compared to colts.

Physiological Differences

• In terms of physiological markers, colts had a greater peak inspiratory and expiratory air flow, peak expiratory tidal volume, and peak minute ventilation.
• However, when adjusted for bodyweight, these values showed no difference between the sexes.

Implications and Follow-Up Research

• The differences in mass-specific peak V̇O between colts and fillies were explained by the differences in their bodyweights.
• The study hypothesises that the variation in peak inspiratory and expiratory air flow, tidal volume, and minute ventilation could be due to smaller lung volumes and airway diameters in fillies, which could result in greater resistance and lower air flows and volumes.
• The study recommends further research to explore these differences and understand how they may change as horses mature and the impacts these may have on performance.