Heterosis among Inbred Lines of Hereford Cattle for Preweaning and Weaning Traits

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PREWEANING and weaning data were collected on 163 Hereford calves to estimate heterosis from linecrossing. Comparisons of the three inbred lines as lines of sire and dam were made to determine if the lines differed in levels of performance after approximately three generations of selection for similar traits. Birth weight, preweaning average daily gain, conformation score at 227 kg and condition score at 227 kg were analyzed separately by sex using least-squares procedures to estimate the effects of year, line of sire, line of dam, line-of-sire × line-of-dam interaction, sires nested within line of sire and the covariables age of dam, inbreeding of dam and birth date of the calf. Differences among the lines in growth rate and conformation score were evident with progeny from line 1 sires and dams generally excelling the other two lines. From comparisons of specific line-of-sire vs. line-of-dam means, it was noted that line 1 dams exhibited excellent maternal ability. Bull progeny from line 1 dams grew significantly faster than bull progeny from line 1 sires and line 1 dams consistently ranked first for preweaning average daily gain when compared to line 2 and 3 dams. Differences among reciprocal linecrosses were generally small and nonsignificant. There was little evidence of heterosis in any of the linecrosses as only one significant positive estimate was obtained; birth weight of the 2 × 3 and 3 × 2 bull calves. Combined heterosis estimates of all crosses by sex for birth weight, preweaning average daily gain, conformation score at 227 kg and condition score at 227 kg were 2.6, 8.2, −.62 and −1.4% for bull calves and −8.2, −3.2, −1.5 and −1.0% for heifer calves, respectively.