Heterosis among Closed Lines of Hereford Cattle I. Preweaning Growth and Survival

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Abstract
Records on 637 crossline and straightline calves produced from all possible reciprocal crosses and straightline matings among five closed lines of Hereford cattle were analyzed. Traits studied were birth and 180-day weight, percentage born and weaned and net kilograms weaned. Line of sire and line of dam were usually significant sources of variation except for birth weight. Line of sire and line of dam ranked about the same for all traits except 180-day weight. Genetic correlations between transmitted and maternal effects were -.58 for birth weight, -.80 for 180-day weight, .11 for percentage born, .44 for percentage weaned and -.54 for net kilograms weaned. The line of sire × line of dam interaction was significant only for 180-day weight. Heterosis estimates were 3% for birth weight, 3% for 180-day weight, 2% for percentage born, 7% for percentage weaned and 10% for net kilograms weaned. Recovery from inbreeding depression accounted for most of the observed crossline heterosis. Copyright © 1979. American Society of Animal Science . Copyright 1979 by American Society of Animal Science.