Effect of environmental temperature and relative humidity on breathing pattern and heart rate in ponies during and after standardised exercise

A preliminary study attempted to assess the influence of atmospheric conditions on the breathing pattern of ponies. The respiratory airflow, tidal volume, breathing frequency, minute volume, total pulmonary resistance and heart rate of five ponies (257 +/- 9 kg and three to five years old) were measured by a standardised procedure. Data were collected at rest, during a nine minute period of treadmill exercise and during a five minute recovery period. The ambient temperature (degrees C) and relative humidity (%) were recorded at the time of each investigation and the respiratory parameters were divided into two groups according to whether the sum of these measurements was less than 85, ie, the conditions were cold and dry or greater than 85, ie, the conditions were relatively hot and humid. Data for each pony in both conditions were compared. The ambient temperature and relative humidity did not significantly modify the breathing pattern of the ponies either at rest or during exercise. On the other hand the frequency of breathing was significantly higher and the tidal volume and total pulmonary resistance were significantly lower during recovery in hot and humid conditions than in cold and dry conditions, while the minute volume remained unchanged. It was concluded that, during recovery, environmental conditions may modify the breathing pattern of horses. This suggests that in hot and humid weather conditions the respiratory rate may be an unreliable measure of the fitness of a horse and, consequently, that a more complete pulmonary investigation should be undertaken for an assessment of fitness.