Review on status of selection for heat tolerance improvement in Cattle

Abstract

The objective is to review the status of selection for heat tolerance improvement in cattle. Economic losses due to heat stress have been significant. Heat stress occurs when THI greater than the animal’s thermo-neutral zone. Many strategies were suggested and implemented to mitigate heat stress. Among them, breeding for improved heat tolerance could be taken as a cost effective and long term solution of the problem. Animal breeding have showed rapid and appreciable advancement. Nowadays, quantitative based breeding has been complemented with molecular based breeding. Identification of heat tolerant cows could help to improve dairy performance through genetic selection. Several measures have been proposed as criteria to identify heat tolerant animals. Differences in thermal tolerance exist among cattle provide clues to select thermo-tolerant animals using genetic tools. The heritability of rectal temperatures under heat stress conditions in cattle ranged from 0.13 to 0.17. There is also heat shock gene related to thermo-tolerance that was identified and being used as marker in marker assisted selection and genome-wide selection to develop thermo-tolerant breeding bull. Heat tolerance genomic breeding values were developed for Holstein and Jersey bulls with reliability of heat tolerance of 30%. Breeding strategies to improve heat tolerance depend on the production system. The genetic mechanisms of heat-stress sensitive and tolerance should be identified before trying to improve heat resistance in dairy cows and in order to optimize the animal breeding program, it is important to add molecular genetic techniques along with the conventional animal breeding methods.