Germplasm evaluation in beef cattle-cycle IV: birth and weaning traits.

Gestation length, unassisted calving percentage, perinatal mortality, calf crop weaned (survival from birth to weaning), birth weight, and 200-d weaning weight of 2,597 calves born and 2,433 calves weaned are reported for F1 crosses resulting from matings of Angus, Hereford, Charolais, Gelbvieh, Pinzgauer, Shorthorn, Galloway, Longhorn, Nellore, Piedmontese, and Salers sires to Angus and Hereford dams (> or = 3 yr of age) in Cycle IV of the Germplasm Evaluation (GPE) Program at the U.S. Meat Animal Research Center. Hereford and Angus sires included 1) reference sires born from 1963 to 1971 used in previous cycles of the GPE Program, 2) sires born from 1982 to 1985 (1980s), and 3) sires born from 1983 to 1985 used in natural service clean-up matings. Effects of sire breed of calf were significant for gestation length, unassisted calving percentage, birth weight, and 200-d weaning weight. Gestation length was significantly longer for Nellore than for Charolais, Galloway, Longhorn, Piedmontese, and Salers, which were in turn longer than for Hereford-Angus and Shorthorn. Rankings for birth weight tended to be inversely related to those for calving ease, except for Shorthorn and Salers sires, which required low assistance relative to their heavy birth weights. Rankings for 200-d weight among AI-sired progeny were as follows: Charolais (231.3), Nellore (229.7), Salers (225.5), Shorthorn (223.8), 1980s Hereford-Angus (223.1), Piedmontese (220.0), Galloway (209.5), reference Hereford-Angus (210.1), and Longhorn (199.0); differences > or = 6.5 kg were significant.