ABSTRACT This study evaluated the effect of the timing of Y‐sorted sexed semen (SS) insemination after the onset of estrus on reproductive outcomes in beef heifers and examined the influence of AI sires and their sperm DNA fragmentation (%SDF) over time. Angus heifers ( n = 718) from two locations were synchronised using a CIDR + Select‐Synch protocol and blocked by age, body condition score, and reproductive tract score. Heifers expressing estrus were randomly assigned to AI at 12, 20, or 28 h post‐estrus onset using SexedULTRA 4 M semen from one of three bulls. Post‐thaw %SDF at 0, 12, and 24 h was assessed by acridine orange staining. Pregnancy per AI (P/AI) differed by timing: 12 h (45.4%), 20 h (48.1%), and 28 h (56.5%) ( p < 0.05), with the 28 h group achieving significantly higher P/AI than the 12 h group. Stillbirth incidence and gender ratio (bull: heifer) did not differ significantly among groups. No overall difference in P/AI among sires was observed; however, a significant sire × time of AI interaction existed ( p = 0.05), with Bull 2 showing the greatest improvement in P/AI at 28 h (up to 15.2 percentage points higher than earlier times). For Bulls 1 and 2, %SDF increased significantly from 0 to 24 h post‐thaw, while Bull 3 showed no change. These findings indicate that delaying insemination to 28 h post‐estrus enhances P/AI when using Y‐sorted SS, potentially due to improved synchrony with ovulation and reduced exposure to sperm with increasing DNA damage.
Kasimanickam et al. (Fri,) studied this question.