Bos indicus and Bos taurus crossbred dairy cattle in Australia. III.* A climate room test of heat tolerance used in the selection of young sires for progeny testing

Abstract

A heat tolerance test for cattle is described, and the results of its use over a 7 year period in a largescale breeding program are given. Animals were subjected to the test on up to three occasions, each test comprising 1 week in an anteroom at moderate temperature followed by 5 days in a climate room at high temperature. Measurements of sweating and respiratory rates, rectal temperature and feed and water consumption are given. The animals were ranked by means of a total score which was made up of the' sum of a sweating rate score and feed intake score less the sum of a rectal temperature score and respiratory rate score. A significant Spearman's rank correlation coefficient of 0.67 was obtained between the ranking of 44 heifers in two separate series of tests. Comparison of bulls from dams selected and unselected for milk production in a stressful climate showed the bulls from the selected dams to be superior in heat tolerance. In the large-scale breeding program, the test selected bulls with three-eighths or half Bos indicus blood in preference to those with quarter Bos indicus blood; and within the quarter-breds it selected those out of dams bred in herds located in a stressful environment in preference to similar crossbred bulls out of dams bred in a temperate environment.