Pregnancy and offspring sex ratio following insemination with SexedULTRA and conventional semen in cows in a commercial beef operation.

Abstract

Pregnancy rate per AI (PR/AI) and breeding season pregnancy rates between insemination with sexed semen (SS; at 18hr after the onset of oestrus) and conventional semen (CS; at 12hr after the onset of oestrus,) and offspring gender ratio between two groups were compared. Angus cross cows (n=686, during 2019 and 2020 breeding seasons) were oestrus-synchronized using Select-Synch + CIDR protocol and were observed thrice daily for oestrus until 72hr after PGF2α administration. Cows expressed oestrus (n=513) were inseminated with either SS (n=246; SexedULTRA 4M™; y chromosome-bearing sperm) or CS (n=267). Cows (n=173) that failed to express oestrus at 72hr after PGF2α received 100μg of GnRH and CS insemination concomitantly. Two weeks later, cows were penned with natural service sires (bull:cow ratio 1:25) for 45days. Pregnancy was diagnosed 30days after bull removal. Calves' gender was determined at birth. For cows that expressed oestrus, PR/AI did not differ (p>.1) between SS (65.0%) and CS (66.7%) groups. The overall PR/AI differed (p<.05) between SS (65.0%) and CS (56.4%) groups. The natural service PR differed (p<.001) but breeding season PR (p>.05) did not differ between SS vs. CS groups. Bull:heifer gender ratio following AI was 88:12 and 52:48 for SS and CS groups, respectively, with an overall 66:34 ratio. Bull:heifer gender ratio for the two breeding seasons was 79:21 and 52:48 for SS and CS groups, respectively, with an overall 62:38 ratio. In conclusion, the fertility of SS insemination at 18hr after onset of oestrus was 97% of CS insemination at 12hr after onset of oestrus. Though breeding season pregnancy did not differ between SS and groups, preferred calf gender was 25 percentage points greater for SS over CS application. The gender accuracy was 88%.