Modified ventilated capsule for the measurement of sweating rate in the exercising horse

Modification of a ventilated capsule technique for the measurement of sweating rate (SR) is described for application in an exercising horse. The plastic capsule was sealed against the coat of the horse. Dry air was blown through the capsule over the skin and the change in absolute humidity (g/m3) between air entering and leaving the capsule was used to calculate SR. The effect of flow rate on the response characteristics of the system was investigated and measured over a range of sweating rates in a group of horses completing a short exercise test. Repeatability of SR measurements made at 2 sites, one 10 cm distal to the tuber sacrale (SRS) and the other approximately overlying C4 in the neck (SRN), were compared. To encourage the rapid and complete evaporation of moisture from the area of coat enclosed by the SR capsule, it was demonstrated that the degree of saturation of the air leaving the capsule should be maintained below 15% relative humidity (RH). This was best achieved at flow rates exceeding 35 l/min. No significant difference was found between the 2 repeated tests separated by 3 days, with respect to right atrial temperature (TRA) and SR. The modified system for the measurement of SR in the exercising horse used in this study was shown to be fast responding and capable of measuring a wide range of sweating rates. A good seal was maintained throughout and the capsule was removed without causing damage to the coat.