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 (ΔI), in standard measure, in the three lines were: Weaning weight line (WWL): Sire: ΔI = .22 BW + .65 WW + .32 YW + .01 MS = 1.65, Dam: ΔI = .09 BW + .84 WW + .12 YW + .07 MS = .44. Yearling weight line (YWL): Sire: ΔI = .07 BW − .05 WW + 1.00 YW − .01 MS = 1.80, Dam: ΔI = .17 BW + .26 WW + .68 YW + .10 MS = .34. Index line (IXL): Sire: ΔI = .16 BW + .15 WW + .40 YW + .62 MS = 1.85, Dam: ΔI = .21 BW + .09 WW + .77 YW + .13 MS = .43.
Published Version
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