AbstractTo further identify factors which influence pregnancy rates, three experiments were conducted to determine the effect of insemination time on sperm transport, fertilization rate, and embryo quality. All cows were continuously monitored for behavioural oestrus by HeatWatch®, and received AI at heat onset (0 h after the first standing event), 12 h after onset, or received natural service at 0 hfrom one of three bulls (Exp. 1). In Exp. 2, cows received AI at 0 h, 12 h, or 24 h after the first standing event. On d 6 after insemination 115 embryos(ova) (Exp. 1) and 117 embryos(ova) (Exp. 2) were recovered from single-ovulating cows. For Exp. 1, median accessory sperm values were: 1 (0 h), 10 (12 h), 27 (natural service O h) (P < 0.05). For Exp. 2, median accessory sperm values were: 1 (0 h), 2 (12 h), 4 (24 h) (P < 0.05). Fertilization rates were: 67% (0 h), 79% (12 h), 98% (natural service O h) (P < 0.05)(Exp. 1); and did not differ in Exp. 2. Embryo quality was not different in Exp. 1. In Exp. 2, percentages of excellent and good fair and poor, and degenerate embryos were: 77, 15, 8 (0 h), 52, 38, 10 (12 h), 47, 19, 34 (24 h) (P < 0.05). In Exp. 3, 30 cows were superovulated and were inseminated once at either 0 h, 12 h, or 24 h after the first standing event. On d 6 after insemination, 529 embryos(ova) were recovered. Fertilization rates were: 29% (0 h); 60% (12 h); 81% (24 h)(P < 0.01). Percentages of embryos with accessory sperm were: 5 (0 h); 8 (12 h); and 41(24 h) (P < 0.01). Embryo quality was not affected by time of AI. We conclude that the time of insemination affects: 1) sperm transport as measured by median accessory sperm number (Exp. 1 and 2) and the percentage of embryos with accessory sperm (Exp. 3); 2) fertilization rate (Exp. 1 and 3); and embryo quality (Exp. 2).
In-vitro matured metaphase-I oocytes have a lower fertilization rate but similar embryo quality as mature metaphase-II oocytes after intracytoplasmic sperm injection
