LIFETIME REPRODUCTIVE EFFICIENCY OF FIRST-CROSS BEEF COWS UNDER CONTRASTING ENVIRONMENTS

Abstract

A population of 1150 first-cross females representing the Hereford-Angus (control) and nine crosses produced by mating bulls of the Charolais (C), Simmental (S), and Limousin (L) breeds with cows of Hereford (H), Angus (A) and Shorthorn (N) breeding provided the data base for breed-cross comparisons of lifetime reproductive performance under two contrasting environments. These data comprised 6022 mating opportunities and 5053 pregnancies recorded during a period that commenced with the breeding season of 1971 and terminated at weaning in the fall of 1979.There were substantial location differences in all performance criteria with the relatively stringent range environment (Manyberries, Alberta) resulting in greater cow losses, lower conception and weaning rates, and less weight of calf weaned than occurred under semi-intensive pasture management (Brandon, Manitoba). Barren culls comprised the largest proportion of cow losses with sire breed ranking C < S < L and dam breed ranking A < H < N for the exotic crosses at both locations. The C cross also ranked lowest for total attrition and highest for percentage conception and percentage of calves weaned per mating opportunity at each location. At Manyberries, these elements of performance combined to give C cross dams a slight advantage in weight of calf weaned per mating opportunity (143 vs. 139 kg for S cross dams), but this ranking was reversed at Brandon (176 vs. 181 kg for S cross). First-cross dams out of A cows at Manyberries ranked above the N cross in weight of calf weaned (139 vs. 135 kg), but this position was reversed at Brandon (172 vs. 176 kg). These changes in ranking at the two locations (C vs. S and A vs. N) may have reflected differences in the degree of environmental stress imposed by the lactation process. All of the sire breed (C, S, L) and dam breed (H, A, N) combinations ranked above the HA control for weight of calf weaned per mating opportunity. However, for this measure of productivity the L vs. HA difference at Manyberries (125 vs. 124 kg) was negligible.