J. Anim Sci.
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J. Anim Sci. 1985. 60:1373-1384.
© 1985 American Society of Animal Science
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Selection for Increased Weaning or Yearling Weight in Hereford Cattle. I. Measurement of Selection Applied1,2,

R. R. Frahm, C. G. Nichols3 and D. S. Buchanan

Oklahoma State University, Stillwater 74078

Abstract

Selection was applied from 1964 to 1978 for increased weaning weight (WWL) or yearling weight (YWL) in two Hereford lines with an Angus line maintained as an unselected control line (CL). Each line was maintained with 50 cows and four sires (two sires selected each year and each used for 2 yr). 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). After 15 yr of selection, a total of 3.22 generations of selection had occurred in both WWL and YWL. Average selection differentials in standard measure per generation for WWL, YWL and CL, respectively, were: BW, .44, .51, .0; WDG, .95, .81, .09; WW, .97, .85, .09; WG, .66, .57, .09; WC, .60, .38, –.02; YDG, .30, .79, .38; YW, .80, 1.05, .25; YG, .63, .62, .34 and YC, .45, .64, .24. The proportionate contribution of sire selection ({Delta}AS) to the average midparent selection differential per generation ({Delta}M) was 70% in WWL and 76% in YWL. Selection indexes in retrospect were also calculated.

Footnotes

1 Journal Article 4560 of the Agr. Exp. Sta., Oklahoma State Univ., Stillwater. Research was conducted by the Anim. Sci. Dept. (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 committees during most of the experiment and the dedicated assistance of the herdsmen and numerous graduate students.

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






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Copyright © 1985 by the American Society of Animal Science.