– R. N. Funston and T. L. Meyer, University of Nebraska, The Professional Animal Scientist 28:560–563 (Condensed by Steve Boyles, OSU Beef Extension Specialist)
Sex-sorting sperm relies on the fact the bovine X chromosome has 3.8% more DNA than the Y chromosome. However, the process of sorting does damage sperm and reduces fertility when compared with conventional semen. Calves resulting from sexed semen do not exhibit more genetic abnormalities nor does it affect calf characteristics.
Five hundred Heifers were fed melengestrol acetate (MGATM) per animal for 14 days. Prostaglandin F2alpha (LutalyseTM) was administered 19 days later and heat detection patches were placed on tail heads. Heifers were artificially inseminated approximately 18 to 24 hours following detection of standing estrus to place insemination closer to ovulation, due to sperm damage in the sex-sorting process. Artificial insemination closer to the time of ovulation has resulted in greater artificial insemination pregnancy rates when utilizing sexed semen in other studies. Heifers not detected in estrus by 72 hours after prostaglandin injection were time inseminated and given a GnRH injection 77 to 78 hours post-prostaglandin injection. Heifers were artificially inseminated with 1 of 2 sires.
Heifers were identified as pregnant by AI, clean-up bull, or nonpregnant. Pregnancy rate was greater for heifers inseminated with conventional compared with sexed semen. These results agree with previous research indicating pregnancy rates using sexed semen are generally 60 to 90% of conventional semen. In addition, more (P < 0.01) heifers detected in standing estrus were pregnant (55.9%) than time inseminated heifers (24.0%).
A review article indicated most inseminations with sexed semen have been conducted at 12 or 24 hours after observed standing estrus, and fertility with timed insemination was lower. Sá Filho et al. (2012) recently reported there were similar AI pregnancy rates for sexed and conventional semen if cows had a greater than 9-mm follicle at the time of insemination.
Pregnancy rates using sexed semen in this study were not different between sires. However, others have reported a difference in fertility rates among bulls when using sexed semen.
Breeding costs based on breeding system were highest for AI with sexed semen (Table 2). A portion of the pregnant heifers (n = 417) were marketed following the breeding season. Heifers pregnant by AI were sold at $1,344/animal, and heifers pregnant by natural service sold at an average of $1,238/animal. Gender difference for replacement heifers AI with sexed semen was not considered as all AI pregnant heifers sold for the same price.
Data from the present study would not support utilization of sexed semen for the clean-up/time AI breeding. Perhaps a combination of utilizing sexed semen to inseminate heifers exhibiting estrus and less expensive conventional semen for the clean-up would decrease the cost difference per pregnant heifer.