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

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