Cold air-induced late-phase bronchoconstriction in horses.

The research investigates how submaximal exercise performed in cold conditions can adversely affect the respiratory health of horses, leading to airway obstruction occurring several hours after the exercise.

Objective and Methodology

The primary objective of this study was to identify the impact of performing exercise in cold conditions on the respiratory system of horses. The potential negative impacts on respiratory health, particularly bronchoconstriction (narrowing of the airways), were assessed.

• The study involved 8 healthy horses which were subjected to 15 minutes of submaximal exercise challenge. It was a random crossover design where the horses alternated between different conditions.
• The independent variable in this study was the temperature of the air the horses were breathing during the exercise, either 25°C which might be considered ‘normal’ or -5°C which would be seen as cold.
• The dependent variables were total respiratory impedance, resistance, and reactance recorded at 5, 24 and 48 hours post exercise, compared to baseline measurements taken before the challenge.

Results and Conclusion

• The results indicated that the temperature of the inspired air did not significantly affect any respiratory mechanical parameters 5 hours after the exercise challenge.
• However, it was observed that cold inspired air was associated with higher respiratory impedance and resistance 48 hours after the exercise challenges. Impedance and resistance are measures of the difficulty encountered in the movement of air in the respiratory pathway.
• This demonstrates that submaximal exercise while breathing very cold air can adversely affect the respiratory mechanisms in healthy horses. The bronchoconstriction caused by exercise in cold conditions could lead to what is referred to as “late phase airway obstruction” which becomes apparent several hours after exercise.
• Interestingly, the time taken for the development of abnormal respiratory mechanical properties in horses was found to be longer than that reported in other mammals.
• The findings of this study suggest that performing exercise routine in cold weather could be a common cause of lower airway disease in horses. Thus, it is important to consider the temperature at which horses are being exercised to prevent potential respiratory issues.