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Selection for Increased Weaning or Yearling Weight in Hereford Cattle. II. Direct and Correlated Responses^1,2,

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. An Angus line was maintained as an unselected control line (CL). Each line was maintained with 50 cows and four sires each year (two sires selected each year and used for 2 yr). Primary traits measured in the lines 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). Averaged over two methods, estimated genetic responses/generation (in standard deviation units) in WWL and YWL were: BW, .29, .26; WDG, .17, .15; WW, .22, .19; WG, .19, .26; WC, .12, .12; YDG, –.02, .04; YW, .08, .14; YG, .19, .16; YC, –.13, –.03. The realized heritability estimates were .23 and .15 for WW and YW, respectively. The realized genetic correlation between WW and YW was .69. Progeny from crosses of selected WWL and YWL sires to Angus cows had similar feedlot and carcass performance. At the end of the study, milk yield and composition were similar for mature cows in WWL and YWL.

¹ Journal article 4561 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 committee during most of the experiment and for the dedicated assistance of the herdsmen and numerous graduate students.

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