Selection Intensities and Time Trends for Performance Traits in Range Hereford Cattle under Mass and Recurrent Selection

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Abstract
Data on selection intensities and time trends in three inbred Hereford lines and their linecrosses resulting from matings to a common tester line produced at the North Montana Branch Experiment Station, Havre, Montana, were evaluated and discussed. Within-line selection was fairly intense in the three inbred lines and test line for weaning weight, postweaning daily gain, and final weight off feed. Selection pressure was much greater on the male side with the bulls used averaging about one standard deviation above the mean of the unselected population. Direct selection pressure for combining ability in the recurrent selection phase was negligible. Phenotypic time trends computed by regression of the traits on years indicated a negative trend in birth weight, weaning weight, and postweaning daily gain in the heifers, and a positive trend in postweaning daily gain of bulls and steers. Environmental trends for birth and weaning weights obtained from repeat mating information indicated a negative time trend. Estimates of genetic progress were positive for birth and weaning weights and were somewhat larger than expected. In general, those lines in which selection was most intense showed the greatest estimated genetic progress. Copyright © 1964. American Society of Animal Science . Copyright 1964 by American Society of Animal Science