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Genetic and Phenotypic Relations Associated with Preweaning and Postweaning Growth of Hereford Bulls and Heifers¹

University of Nebraska, Lincoln 68503 and U. S. Department of Agriculture

Abstract

Data from 3,462 Hereford calves were analyzed. Birth weight and preweaning daily gain were 7 to 8% higher in bulls than in heifers. Heritabilities of traits were consistently smaller for bulls than for heifers. The heritabilities, giving bulls first and heifers second, were: birth weight, 49 and 57%; daily gain to 135 days, 15 and 17%; daily gain to weaning, 13 and 21%; 200 day weight, 15 and 25% daily gain postweaning, 29 and 65%; and 452 and 550 day weight, 23 and 52%.

Genetic and phenotypic correlations among traits were presented. Birth weight was more closely correlated with postweaning daily gain (r_G=0.42 and 0.30, r_p=0.31 and 0.34 for bulls and heifers) than it was with preweaning daily gain (r_G=0.10 and 0.28, r_p=0.18 and 0.27 for bulls and heifers). Preweaning daily gain was not closely related with postweaning gain in bulls (r_G=0.14, r_P=0.15). In heifers the genetic correlation between pre and postweaning gain was much higher (r_G=0.47) than the phenotypic correlation (r_p=0.07). These results indicate differential weight should be given to bull or heifer records in assessing genetic merit of individuals or parents.

¹ Department of Animal Science, published as Paper Number 3376, Journal Series, Nebraska Agricultural Experiment Station. Contribution from North Central Regional Project NC-1, Improvement of Beef Cattle Through Breeding Methods.

² Department of Animal Science, University of Nebraska, Lincoln 68503.

³ Beef Cattle Research Branch, Animal Science Research Division, A.R.S., Lincoln 68503.

⁴ U. S. Meat Animal Research Center, Animal Science Research Division, A.R.S., U.S.D.A.

⁵ The authors gratefully acknowledge assistance of the late J. E. Ingalls, W. W. Rowden, J. A. Rothlisberger and R. D. Humphrey in supervision of livestock operations and collection of data.