Heterosis in Preweaning and Weaning Traits among Lines of Hereford Cattle

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Abstract
Data on 241 bull and 228 heifer calves collected at the U. S. Range Livestock Experiment Station, Miles City, Montana, were used to estimate the amount of heterosis resulting from linecrossing within the Hereford breed. Cattle from 5 inbred lines were mated to produce all possible straightline and crossline combinations in each of the years 1962 through 1965. Records on birth weight, preweaning daily gain, weaning weight and weaning score were analyzed by least-squares procedures. The effects studied were line-of-sire, line-of-dam, line-of-sire×line-of-dam, years, line-of-sire×year, line-of-dam×year, age of dam and lactation status the previous year. Differences among the lines in growth traits and maternal ability were evident from the analyses of variance and the line-of-sire and line-of-dam adjusted means. Greater heterosis was exhibited for preweaning daily gain and weaning weight than for birth weight or weaning score. Heifer calves exhibited more heterosis for preweaning daily gain and weaning weight than bull calves. Heterosis for birth weight, preweaning daily gain, weaning weight and weaning score amounted to 3.0, 5.6, 5.1, and 2.5% for bull calves and 3.8, 10.6, 9.4, and 2.7% for heifer calves, respectively.

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