PERFORMANCE OF HEREFORD AND 2-BREED ROTATIONAL CROSSES OF HEREFORD WITH ANGUS AND SIMMENTAL CATTLE .1. CALF PRODUCTION THROUGH WEANING

Cow size, reproductive traits and calf performance through weaning were evaluated in a range environment for Simmental (S) x Hereford (H) and Angus (A) x H crosses in two-breed rotations and straightbred H. Data were grouped into seven dam breed categories: straightbred Hereford (H), crossbred F1 S x H cows (SH), S x H cows of low percentage H (SHS), S x H cows of high percentage H (HSH), F1 A x H cows (AH), A x H cows of low percentage H (AHA) and A x H cows of high percentage H (HAH). Straightbred H, SH, AH, SHS and AHA cows were mated to H bulls, HSH cows were mated to S bulls and HAH cows were mated to A bulls. Cows in the SHS and AHA groups ranged from 1/4 to 3/8 H and their calves from 5/8 to 11/16 H. Cows within the HSH and HAH groups ranged from 5/8 to 3/4 H and their calves from 5/16 to 3/8 H. Cow age ranged from 3 to 10 yr. Simmental-cross cows were heavier and taller and produced heavier calves at birth and weaning than A-cross. Pregnancy rate, calf birth date and percentage of difficult births did not vary significantly among dam breed groups. Within the A x H and S x H rotations, dam breed group rankings for calf birth weight were inverse to rankings for proportion of H in the breed makeup of the calf. However, rankings of SHS vs HSH and AHA vs HAH dam breed groups for calf ADG were the same as rankings for proportion of H in the breed makeup of the calf and thus were inverse to rankings for proportion of H in the dam. Evaluation of different breed groups within the two-breed rotational crossbreeding systems suggested that compatibility of S with H and A with H was acceptable in rotational breeding systems with regard to mature size and calving difficulty among 3- to 10-yr-old cows. Intergenerational variation for cow size within a rotation appeared to be sufficiently small so that cows of various breed compositions within a rotation could be managed adequately as a single group.