Field Trial Assessing the Use of Sex-Sorted Semen in Beef Cattle

Sex-sorted semen utilization holds the potential to create a high percentage of either bull or heifer calves, but often comes with a reduction in fertility.The objective of this study was to evaluate the reproductive performance of sex-sorted semen (both X-and Y-sorted semen) in commercial beef cows and heifers.For this trial, 320 Angus and SimAngus cows and heifers from four groups were used.The groups were: yearling heifers (Group 1, n = 101); young cows (Group 2, n = 51) bred to an Angus sire sorted for >90% X-bearing sperm; and 168 mature cows (Group 3, n = 80; and Group 4, n = 88) bred to a Charolais sire sorted to contain >90% Y-bearing sperm.Heifers were synchronized using melengestrol acetate plus prostaglandin F 2α (MGA-PGF 2α ) and were bred based on visual estrus detection.The three cow groups were synchronized using the 7-Day CO-Synch plus CIDR protocol.Group 2 young cows and Group 3 mature cows were inseminated using a split-time artificial insemination (STAI) approach, while Group 4 mature cows were inseminated using a fixed-time AI (FTAI) approach.The estrus responses were: 95.1% (Group 1), 88.2% (Group 2), 75.0%(Group 3), and 69.3% (Group 4).The AI pregnancy rates were: 63.4% (Group 1), 47.1% (Group 2), 46.3% (Group 3), and 40.2% (Group 4).The Group 1 heifers had a high estrus response and AI pregnancy rate likely due to the inherent fertility of heifers and intensive estrus detection used.The AI pregnancy rates for the Group 2 young cows and Group 3 mature cows were similar to what is seen in the literature.Group 4 mature cows' decreased estrus response and AI pregnancy rate were lower than reported in other studies.Finally, the Charolais sired calves averaged around 100 lb heavier than their Angus sired counterparts.These results show the commercial potential of using "bull" sex-sorted semen in terminal sire programs.