Two-, three- and four-breed rotational crossbreeding of beef cattle: reproductive traits

Reproductive data were collected on 4,596 cow exposures in a rotational crossbreeding study that spanned four generations (1970 through 1988). Angus (A), Brahman (B), Charolais (C) and Hereford (H) breeds were included in three two-breed (A-B, C-B and H-B), three three-breed (A-B-C, A-B-H and C-H-B) and one four-breed (A-B-C-H) rotational mating system. Contemporary straightbreds were produced each generation. Reproductive traits of interest were calving rate, calf survival, weaning rate, calf birth date and calving assistance. Overall means and standard errors for calving rate, calf survival, weaning rate, calf birth date and calving assistance were 82.1 +/- .6%, 92.8 +/- .4%, 76.2 +/- .6%, 50.4 +/- .3 d and 4.2 +/- .3%, respectively. Rotational mating systems had similar calving and calf survival rates that were greater (P less than .01) than those of straightbreds. Three- and four-breed rotation systems had similar weaning rates (81.5 +/- 1.1 and 80.8 +/- 2.0%) that were higher than those for two-breed rotations (77.1 +/- 1.2%). Two- and three-breed rotation systems had fewer assisted births (3.5 +/- .6 and 2.2 +/- .6%) than straightbreds (5.5 +/- .6%) and the four-breed rotation (5.4 +/- 1.0%). Three-breed rotation calves were born earlier in the calving season (46.8 +/- .6 d; P less than .05) than straightbred, two-breed or four-breed rotation calves (51.8 +/- .6, 52.1 +/- .6 and 51.1 +/- 1.0 d). Hereford-Brahman two-breed rotation cows had higher (P less than .05) calving and weaning rates than A-B or C-B two-breed rotation cows (87 +/- .4 vs 81.9 +/- 1.9 and 81.5 +/- 1.8%; 81.7 +/- 2.0 vs 76.4 +/- 2.1 and 74.1 +/- 2.0%). All three-breed rotation combinations had similar calving, calf survival and weaning rates, assistance at calving and calf birth dates. Rotational combinations tended to be more superior (P less than .05) to weighted purebred means for calving, calf survival and weaning rates than for calf birth date and calving assistance.