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Genetic and Environmental Influences on Gain of Beef Cattle during Various Periods of Life¹

Iowa State University, Ames^{,3, 4,}

Abstract

The effects of sex, year, age of dam and age of calf at weaning were evaluated for gain in Hereford bull and heifer calves during different time periods up to one year of age. The least squares constants for the effects of age of dam and weaning age indicate that age of dam and perhaps weaning age should be considered in evaluating calves for post-weaning gains. These data suggest that different regressions of weaning weight on age of calf should be used for bulls and heifers to adjust weaning weight for age at weaning.

Heritability was 0.25 for weaning weight, 0.40 for 140-day feedlot gain and 0.47 for weight at a year of age. These estimates agree reasonably well with previous estimates in the literature. They indicate that considerable progress should result from selection for rate of gain. If the relatively high heritabilities of early feedlot gains as compared with those made later during the post-weaning period should be verified in later studies, measurement of gaining ability can be made at relatively young ages. The large genetic correlations between gains made in different periods suggest that the same genes are largely responsible for gains made during the first year.

¹ This Paper Represents Part of a Dissertation Submitted by the author to the Graduate School, Iowa State University, in partial fulfillment of the requirements of the Degree of Doctor of Philosophy in Animal Breeding. Acknowledgement is made to C. E. Haigler for use of the data and to Dr. L. N. Hazel for assistance in its preparation.

² Present address: U. S. Department of Agriculture, Agricultural Research Service, Animal Husbandry Research Division, Beef Cattle Research Branch, University of Nebraska, Lincoln, Nebraska.

³ Journal Paper No. J-3936, of the Iowa Agricultural and Home Economics Experiment Station, Ames, Iowa. Project Number 1055.

⁴ Contribution from the North Central Regional Project NC-1.

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