J. Anim Sci.
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J. Anim Sci. 1977. 44:352-359.
© 1977 American Society of Animal Science
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Selection for Postweaning Growth Rate in a Closed Line of Hereford Cattle1

David J. Chevraux2 and Curtiss M. Bailey3

University of Nevada, Reno 89557

Abstract

Selection applied and estimated genetic response were studied in a closed line of registered Hereford cattle selected for increased gain during a 140-day postweaning test. Data included weaning weights (N = 414) and postweaning gains (N = 390) of calves produced during the period 1955 to 1974. Genetic response in postweaning gain and correlated changes in weaning weight were estimated by two methods: (1) Regression of trait on dam birth year; and (2) Regression of trait deviation on generation coefficient.

During the course of the study, 3.24 generations of offspring had been produced by selected parents. The mean annual selection differential for the primary trait, postweaning gain, was .22 standard deviation units, or alternatively, .93 standard deviation units per generation. The secondary selection differential for weaning weight averaged .06 standard deviation units per year, or .29 standard deviation units per generation.

Direct genetic response in total gain during the 140-day postweaning test evaluated by regression on dam birth year was .34 ± .29 {sigma} units per generation. Estimated response obtained through regression of postweaning gain deviations on generation coefficient was .31 ± .18 {sigma} units per generation. Realized heritability for the primary trait computed from these results averaged .35. The correlated genetic response in weaning weight utilizing the two methods was .13 ± .24 and .20 ± .18 {sigma} units per generation, respectively.

Footnotes

1 Contribution from the Agricultural Experiment Station, University of Nevada, Reno, Journal Series No. 342.

2 Former Graduate Fellow in Animal Science and Professor, respectively.

3 The assistance of the late James E. Hunter, Art Cerfoglio and Robert Barry during the course of the experiment is gratefully acknowledged.






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Copyright © 1977 by the American Society of Animal Science.