Fertility in Beef Cows Bred to Produce Straightbred and Crossbred Calves

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Abstract
This paper reports the results of two trials on the effects of heterosis on certain reproductive phenomena. A total of 917 and 592 observations were involved in trial I and trial II, respectively. In trial I, Hereford, Angus and Shorthorn females were bred to produce both straightbred and crossbred calves and, in trial II, Hereford and Angus females were bred to produce both crossbred and straightbred calves. All straightbred groups and all possible crosses were produced in both trials. The results of trial I showed a slight advantage in reproductive performance for cows bred to produce crossbred calves when compared to those bred to produce straightbred calves. The advantage was greatest for the Hereford X Shorthorn and reciprocal cross. The results were not consistent between the two experiments, since the females bred to produce crossbred calves showed slight disadvantages when compared to females bred to produce straightbred calves in trial II. The results of this study show a small heterotic effect in reproductive phenomena associated with breeding straightbred cows to produce both crossbred and straightbred calves for the Hereford X Shorthorn and reciprocal cross. However, for Hereford X Angus and Angus X Shorthorn reciprocal crosses, heterotic effects were not revealed for the traits studied. Copyright © 1967. American Society of Animal Science . Copyright 1967 by American Society of Animal Science