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An observational study was conducted to evaluate the effect of anterior pituitary gonadtropin on super-ovulation in donors, embryo quality, development stage of embryo, transfer location, corpus luteum quality of recipient, ease of transfer and induced versus natural estrus on pregnancy rates. The data were collected from 451 non-surgical transfers of fresh and frozen bovine embryos. 1. The average number of CL, formed in ovaries which were stimulated with follicular stimulating hormone, and/or APG, were 11. 1±1.21, 12.3±1.84, respectively. The numbers of embryos recovered were 8.2±1.35, 8.7± 1.39, and the numbers of transferable embryos were 6.4±0.98. 6.6±1.01. respectively. 2 There was no effect of spontaneous versus prostaglandin-induced estrus of recipients on pregnany rates of either fresh (61.5% vs. 59.5%) or previously frozen(54.5% vs. 58.5%) embryos. 3. There were significant differences(p<0.05) in pregnancy rates for embryo grade 1(63.6%), grade 2 (45.4%) and grade 3 (30.4％) in fresh group and for grade-1 (60.5%), grade-2 (47.8%) and grade-3 (18.1%) in previously frozen embryos. 4. The recipients transfered with embryo morulae were found to have a lower (p<0.05) pregnancy rates than those transfered with embryos of blastocyst in be th fresh and previously frozen embryos. 5. There was no significant difference between transfer locations in pregnancy rates using both fresh and frozen embryos. 6. Attempts to select recipients for high pregnancy rates on the basis of corpus luteum (CL) quality were performed. CL were classified into 3 quality grades, on the basis of size and prominence. Quality grades 1 and 2 group had higher (p<0.05) pregnancy rates than grade-3 group using both fresh and frozen embryos. 7 Ease of transfer was ranked to a scale of one to three on the basis of increasing difficulty (time required). Transfers ranted as ease score 1 and 2 had significantly higher (P<0.05) pregnancy pregnancy rates (45.8%, 66.6%) than ease score 3 (27.7%, 31.8%) using both fresh and frozen embryos respectively.
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