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Selection for Growth and Muscling Score in Beef Cattle I. Selection Applied^1,2,

University of Nebraska, Lincoln 68583 and and US Department of Agriculture, Clay Center, NE 68933

Abstract

Selection has been applied in three 150-cow, 6-sire lines of Hereford cattle since 1960 when the lines were formed from a common base. Data through 1977 (1976 for postweaning traits) were available for analysis. The three lines were selected for weaning weight (WWL), yearling weight (YWL) and an index of yearling weight and muscling score (IXL). Traits analyzed were birth weight (BW), preweaning daily gain (WDG), weaning weight (WW), postweaning daily gain (PDG), yearling weight (YW) and muscling score (MS). Through 1977 an average of 3.7, 3.6 and 3.7 generations of selection had been practiced in WWL, YWL and IXL, respectively. Cumulative selection differentials were calculated by adding the individual's own deviation from its contemporary group to the average cumulative selection differentials of the parents of the contemporary group. Cumulative selection in WWL, YWL and IXL, respectively, in the 1977 calf crop (1976 for postweaning traits) was: BW, 2.1, 1.9, 1.9; WDG, 3.3, 2.4, 2.5; WW, 3.5, 2.6, 2.7; PDG, 1.1, 2.8, 2.7; YW, 2.9, 3.4, 3.3 and MS, .8, 1.4, 2.8 standard deviations. Sire and dam indexes in retrospect with their selection differentials/generation (Al), in standard measure, in the three lines were: Weaning weight line (WWL): Sire: Al = .22 BW + .65 WW + .32 YW + .01 MS = 1.65, Dam: Al = .09 BW + .84 WW + .12 YW + .07 MS = .44. Yearling weight line (YWL): Sire: Al = .07 BW - .05 WW + 1.00 YW - .01 MS = 1.80, Dam: Al = .17 BW + .26 WW + .68 YW + .10 MS = .34. Index line (IXL): Sire: Al = .16 BW + .15 WW + .40 YW + .62 MS = 1.85, Dam: Al = .21 BW + .09 WW + .77 YW + .13 MS = .43.

¹ Published as Paper No. 6673 Journal Series, Nebraska Agr. Exp. Sta., Lincoln and a contribution from Regional Project NC—1, Improvement of Beef Cattle Through Breeding Methods.

² Authors express appreciation to L. G. Beerwinkle, G. Hays, J. Loseke, J. Stark, R. Sampson and N. Scott for data collection and to Bradford Knapp and W. Hinerman for data processing.

³ Present address: Anim. Sci. Dept., Oklahoma State Univ., Stillwater 74074.

⁴ Anim. Sci. Dept., Univ. of Nebraska

⁵ Anim. Sci. Dept., Univ. of Nebraska, Roman L. Hruska U.S. Meat Animal Research Center, Clay Center.

⁶ Roman L. Hruska U.S. Meat Animal Research Center, AR-SEA, USDA, Clay Center.

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