Reproduction and calf performance of Angus-sired and Polled Hereford-sired cows bred to Angus and Brahman bulls for primiparous calving as two- vs three-year-olds.

This 4-yr study was conducted with Angus (A)-sired and Polled Hereford (PH)-sired crossbred heifers that were exposed to either A or medium-frame Brahman (B) bulls from primiparous calvings either as 2- or 3-yr-olds. Each year, heifers were allotted at random within breed composition and age of dam to breeding groups on pasture for an 84-d breeding period that began in late March or early April. Results indicated that differences due to age of dam (AOD), calf sire breed (CSB) and dam sire breed (DSB) were similar for calving rate, earliness of calving in the calving period and percentage of calves born alive, percentage weaned of those born alive and percentage weaned of cows exposed. The 3-yr-old cows had less calving difficulty and their calves had higher birth weight, average daily gain (ADG) to weaning, 205-d weight and 205-d weight/cow exposed than the 2-yr-old cows. Compared with the B-sired calves the A-sired calves had lower birth weight, ADG to weaning and 205-d weight; however, 205-d weight/cow exposed was similar. Compared with the PH-sired cows, the A-sired cows had less calving difficulty, and their calves had higher ADG to weaning and higher 205-d weights/cow exposed. Under conditions similar to those of this study, it would be economically advantageous to calve first at 2 yr of age rather than at 3 yr of age.