Abstract Predicted fertility of sires used in artificial insemination programs is based on two semen quality parameters: motility and morphology. While these characteristics are critical for assessing the potential of spermatozoa to reach the egg and complete fertilization, additional factors may further differentiate sire fertility. The longevity of sperm viability within the female reproductive tract could influence the likelihood of fertilization, especially when insemination and ovulation are not ideally synchronized in many timed AI protocols. Therefore, the objective of this study was to evaluate differences in semen viability within the female tract using heterospermic insemination. Semen collected from one Angus sire and one Hereford sire was analyzed for morphology and motility and combined in straws containing equal percentages of motile sperm from each bull. All females at both locations were time-inseminated using the 7-day CO-Synch+CIDR protocol. At location 1, heifers were inseminated 48 hours after PGF injection and CIDR removal. Cows at this same location were inseminated 54 hours after PGF/CIDR removal. At location 2, cows were inseminated 60 hours after PGF/CIDR removal. All females at both locations received a GnRH injection at time of insemination. Blood samples were collected from calves for parentage verification. In both locations, analysis of the confirmed AI-sired calves using a z-test demonstrated a significant difference in Hereford sire contribution (Loc. 1: z-score = -4.22, p ≤ 0.01; Loc. 2: z-score = 6.2, p ≤ 0.01), highlighting a pronounced disparity between the Hereford and Angus bulls at both locations. Further studies are necessary to assess the fertility of AI sires used in timed-AI protocols due to differences in longevity of sperm viability in-utero. This variable could be a factor in selecting sires to maximize calf crops in timed-AI protocols.
Gruis et al. (Wed,) studied this question.