I Effects of Breed-Type and Breeding System on Efficiency of Weaned Calf Production

The objective of this study was to evaluate effects of cow breed-type (two-breed rotations of Simmental x Hereford, Angus x Hereford, and Tarentaise x Hereford) and breeding system (rotational vs terminal sires) on production efficiency to weaning. Cows were limit fed in drylot for one year to simulate weight change of range cows. Both cow breed-type and sire type significantly affected efficiency of weaned calf production (weaning weight divided by cow and calf creep feed ME intake). However, there was an interaction of cow breed-type with breeding system for efficiency of weaned calf production. In particular, Hereford-sired Simmental-Hereford cows had higher weaning efficiency when mated to Simmental (i.e., rotational) bulls than when mated to Charolais (i.e., terminal) bulls. In contrast, cows of other breed-types were more efficient when mated to terminal bulls than when mated to rotational bulls. Because cow breedtype rankings for production efficiency can vary depending on the type of sire to which cows are mated, it is important to consider genetic complementarity in the design of breeding systems. D.M. ~arshall ' Department of Animal & Range