Comparisons of the heat tolerance of Sindi and Jersey cattle and Sindi Jersey crosses in the hot Amazon region. I. The Sindi, 3/4 Sindi 1/4 Jersey and 3/8 Sindi 5/8 Jersey

Abstract

A comparison between pure Sindi, 5/8 Jersey 3/8 Sindi, and 3/4 Sindi 1/4 Jersey steers and heifers was made under the very hot, moist Amazonic environment. The influence of diurnal change (morning and evening), air temperature and air moisture for the two seasons, which are: rainy ("winter") and dry season ("summer") were studied. Rectal temperature, respiration rate, and pulse rate were used as indicators of heat tolerance. It was concluded that the pure Sindi and 3/4 Sindi-Jersey had the best heat regulation. However the pure Sindi had difficulty in maintaining its thermo-regulation under conditions of high moisture and high heat. In 3/4 Sindi-Jersey and 5/8 Jersey-Sindi groups increased respiration rate was the main response to heat stress.