The effect of environmental temperature and humidity on the frequency of the heart beat of Ayrshire calves

Abstract

1. The heart rates of 4-month-old Ayrshire bull calves were measured in individual 6 hr. daily exposures to 15, 20, 25, 30, 35 and 40° C. dry bulb temperatures at 17 mg./l. absolute humidity and at 7 mg./l. saturation deficit at temperatures 30–40° C. The schedule of experiments on each animal lasted 45 days and consisted of five replications of these nine environmental conditions. Throughout the experimental schedule the heart rates of three paired control animals were measured in a temperature-controlled holding room. 2. The heart rates of all experimental animals increased with increasing environmental temperatures above 20° C. and with increasing humidity above 30° C.