J. Anim Sci.
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J. Anim Sci. 1986. 62:54-65.
© 1986 American Society of Animal Science
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Direct and Correlated Responses to Selection for Increased Weaning or Yearling Weight in Angus Cattle. I. Measurement of Selection Applied1,2,

D. K. Aaron3, R. R. Frahm and D. S. Buchanan

Oklahoma State University, Stillwater 74078

Abstract

Four 50-cow, 4-sire lines of Angus cattle weie established as part of a long-term selection project. Performance data through yearling age were coUected on 2,749 calves during the 16-yr period, 1964 to 1979. Lines were selected for individual weaning weight, (WWL), individual yearling weight (VWL) and a combination of individual and progeny weaning weights (PTL). The fourth line was maintained as an unselected control line (CL) to monitor yearly environmental changes. Criteria in the CL were zero selection differentials for both weaning and yearling weights. Traits analyzed were birth weight (BW), preweaning daily gain (WDG), weaning weight (WW), weaning conformation grade (WG), weaning condition score (WC), weaning to yearling daily gain (YDG), yearling weight (YW), yearling conformation grade (YG) and yearling condition score (YC). Over the 16-yr period, 3.87 and 3.72 generations of selection had occured in the WWL and YWL, respectively. The PTL was terminated in 1978, and 2.68 generations of selection had occured to that point. Mean selection differentials in Standard measure per generation for WWL, YWL and CL, respectively, were: BW, .43, .46, .00; WDG, .96, .70, .08; WW, .97, .74, .08; WG, .48, .37, .09; WC, .53, .30, .00; YDG, .11, .86, .37; YW, .67, 1.00, .25; YG, .43, .85, .33; and YC, .22, .48, .23. Selection indexes in retrospect were also calculated.

Footnotes

1 Journal Article 4613 of the Agr. Exp. Sta., Oklahome State Univ., Stillwater. Research was conducted by the Anim. Sci. Dept. (OAES Project 1256) in cooperation with USDA, SEA, Southern Region and contributes to the Regional Beef Cattle Breeding Project NC-1.

2 Authors gratefully acknowledge the keen interest and valuable administrative and technical assistance of D. F. Stephens and J. V. Whiteman. Special thanks are expressed to D. C. Meyerhoeffer for being a regular member of the scoring committee during most of the experiment and to herdsmen and numerous graduate students for their dedicated assistance.

3 Present address: Anim. Sci. Dept., Univ. of Kentucky Lexington, KY 40546.






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Copyright © 1986 by the American Society of Animal Science.