As a means of minimizing dystocia, it has been generally recommended that British yearling heifers not be mated to Continental bulls. However, in recent years, seedstock breeders in the Continental breeds have been putting increased selection pressure on improving calving ease. This has been especially true within the Simmental breed. In this two-year study, Montana State Univ. researchers artificially inseminated commercial Angus yearling heifers on four Montana ranches using semen from 20 high calving ease Simmental and 27 low birth weight Angus sires. Simmental sires were in the top 10% of their breed for calving ease EPD and Angus sires were in the top 10% of their breed for low birth weight EPD. The dataset consisted of a total of 1,038 calvings in the year 2000 and 2001. Simmental sired calves were 2.9 days longer in gestation length and 4.7 lb heavier at birth than Angus sired calves. Percent of assisted births was significantly higher for Simmental sired calves but the difference was not as great as one might expect (41% vs. 29%). The authors concluded that Simmental sires with calving ease EPDs in the top 10% of the breed can be mated to Angus heifers, of Montana origin, with only 10 to 15% increase in assistance rate over that of Angus sires in the top 10% for low birth weight EPD. Furthermore, as a result of both heterosis and breed complementarity, the crossbred calves would be expected to have heavie weaning weights and greater post-weaning rates of gain. As sexed semen technology advances, yearling heifers could be bred to female sperm, which would further reduce the incidence of dystocia (Van Wagoner et al. 2003. Proc. Western Section ASAS, 54:159).