To study the effects of ibaraki virus on preimplantation mouse embryos collected from prepubertal ICR and BALB/cByJ mice (30-40 days old) by superovulation, zona pellucida-intact (ZPI) or free (ZPF) embryos (n=774) of 4- to 8-cell and morulae were exposed to 10** (5.8) TCID50 of the viurs up to 96 hours. The embryos were examined morphologically by observing the degeneration and hatching rates, and virologically and immunologically by determining the presence of infection with the virus, in addition, the effect of washing the embryos to remove virus possibly attached to was also investigated. The ZPI 4- to 8-cell embryos and morulae exposed to the virus showed considerably higher degeneration rate than those not exposed, for 96, and for 72 to 96 hours, respectively (p0.01). The ZPF 4- to 8-cell embryos and morulae exposed to the virus showed considerably higher degeneration rates than those not exposed, throughout the whole culture hours in vitro (p0.01). The ZPI 4- to 8-cell embryos and morulae not exposed to the virus showed considerably higher rates of hatched blastocyst than those exposed (p0.01). The virus infection rates of the ZPF 4- to 8-cell embryos and morulae were significantly higher than those of the ZPI embryos according to cell culture system. The viral antigen was detected exclusively on the zona pellucida of ZPF embryos by the immunofluorescent assay. In the ZPI embryos exposed to ibaraki virus, the virus was detected in the two times-washing groups, but not in the ten times-washing groups. The results indicated that zona pellucida of murine embryos would provide an effective protection and that ten times-washing of the ZPI embryos previously exposed to the virus was effective to remove virus from the embryos

This study was performed to investigate the effects of stage and quality of embryo, synchrony between donor and recipient and difficulty of transfer on pregnancy rate following non-surgical transfer of frozen-thawed bovine embryos. The overall pregnancy rate of this experiment was 63.4 % and that of heifers (73.1 %) was higher than that of cows (46.7 %). The pregnancy rates of recipients transferred with morulae, early blastocysts and blastocysts were 50.0 %, 64.7 % and 71.4 %, respectively. The pregnancy rate of recipients transferred with good embryos (67.9 %) was higher than that of recipients transferred with fair embryos (53.8 %). The pregnancy rates of embros transferred to left and right uterine horn were 63.2 % and 63.6 %, respectively. The pregnancy rate of recipients in estrous synchrony 0 (76.2 %) was higher than those of recipients in synchrony -1 (55.6 %) and +1 (44.4 %). The pregnancy rate of recipients transferred with 2 embryos (71.4 %) was higher than that of recipients transferred with 1 embryo (61.8 %). The pregnancy rate of embryos transferred to uterine tip (72.0 %) was higher than that of embryos transferred to uterine base (50.0 %). Ease of transfer was ranked to a scale of one to three on the basis of increasing difficulty. Transfers ranked as ease score 1 accounted for 77.8 % of pregnancies and had higher pregnancy rate than ease score 2 (66.7 %) or 3 (45.5 %). The pregnancy rate of recipients with excellent corpus luteum (CL) (70.0 %) was higher than those of recipients with good CL (61.1 %) or fair CL (61.5%). In reviewing above results, it was considered that the factors such as embryo stage, embryo quality, estrous synchrony, corpus luteum quality, tranfer site within uterus, recipient's parity and ease score affected the pregnancy rate after non-surgical transfer of frozen-thawed bovine embryos