Improving Tropical Beef Cattle by Simultaneous Selection for Weight and Heat Tolerance. Heritabilities and Correlations of the Traits1

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Abstract
The possibility of selection of beef cattle simultaneously for weight gain and heat tolerance traits is examined. A group of 192 bullocks and heifers were exposed for about 7 hr. to direct sun in a pen. Temperature and respiratory rate were taken before and after heat treatment, the haemoglobin level being recorded also, together with average daily weight gain from weaning to 18 months of age. The data were analysed by least squares methods, considering as effects on the model: sex, haemoglobin type, coat color, day of observation, age, and sires. The results include heritability estimates for the initial rectal temperature (.11±.16), increase in rectal temperature (.44±.27), initial respiratory rate (.59±.28), logarithm of the increase in respiratory rate (.44±.2 7), haemoglobin level (.55±.27), and rate of daily weight gain after weaning (.46±.25). Genetic, phenotypic, and environmental correlations of the six traits were estimated. The results indicated no relationship of the haemoglobin type to heat tolerance. The possibility of joint selection for weight and heat tolerance traits is suggested with the recommendations of omitting haemoglobin level. Copyright © 1973. American Society of Animal Science. Copyright 1973 by American Society of Animal Science.

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