Secondary Selection Differentials for Cow Productivity Traits Associated with Seven Criteria of Selecting Replacement Beef Heifers

Abstract

Effects of selection for each of seven calfood traits on later adult performance for conception rate and progeny weaning weight ratio were examined in an unselected population. Data on calfhood traits and lifetime productivity traits of 144 Angus cows based on records of 855 progeny were analyzed by least squares methods. Cows were classified as first through fourth quartile with regard to each of seven calfhood traits (weaning weight ratio, preweaning relative growth rate, postweaning daily gain ratio, postweaning relative growth rate, yearling weight ratio, birth to yearling relative growth rate and conformation score). Selection differentials for each calfhood trait and correlated secondary selection differentials for cow productivity traits were estimated. Selection based on weaning weight ratio, yearling weight ratio or postweaning daily gain ratio of a female tended to increase weaning weight of her progeny while producing small and generally negative effects on her reproductive efficiency as a cow. Relative growth rate was negatively related to reproductive measures while producing negligible effects on progeny weaning weight. Conformation score as a basis for selection produced no significant effects on cow productivity. Cow productivity traits were lowly correlated with calfhood measures of performance. Copyright © 1979. American Society of Animal Science . Copyright 1979 by American Society of Animal Science.