Frozen embryos with highest genetic-potency were imported from America in cooperation with the Holstein-Friesian of America and transferred to the recipients in the National Animal Breeding Institute. The estrus synchronization were induced with 64 cows by intramuscular injections of 25㎎ PGF₂α between 11 days interval. The frozen embryos thawed at 32℃ were rehydrated within the medium at 5 steps in order to remove glycerol. The embryos were transferred to 30 recipients with surgical method and the results were as follows: 1. Among 64 cows, heat inducing rate after 1st and 2nd injections of PGF₂α was 53.1 and 76.6%, respectively. 2. Most of synchronized estrus was induced within 2-4 days after PGF₂α injections, however prevalent one was within 3 days. 3. Heat inducing rate after 1st and 2nd injections of PGF₂α was 35.5 and 77.4% in the heifer and 69.7 and 75.8% in the cow. The rate after 2nd injection was much higher than 1st injection and the cow showed much higher rate than the heifer in 1st injection. 4. Among 30 recipients, 20 cows (66.7%) has corpus luteum in right ovary and 10 cows (33.3%) in the left. Three cows in 16 cows with A-class CL, 7 cows in 12 cows with B-class CL and 1 cow in 2 cows with C-class CL showed highest conception rate. 5. The frozen embryos staged from late morula to expended blastocysts were transferred and concepted. Conception was possible even in the C-class embryo. 6. Among 30 recipients, 11 cows (36.7%) were concepted and the cows (37.5%) showed slightly higher conception rate than the heifer (36.7%). 7. The conception rate of frozen embryo was 1 S.8% in first trial with 6 steps glycerol equilibration, 16.7% in 2nd trial with 2 steps sucrose equilibration and 36.7% in this 3rd trial with S steps glycerol equilibration. Third trial showed highest conception rate. 8. Among 79 recipients, 26 cows (32.9%) were concepted and farrowed. The conception rate of fresh embryos (55.6%) was higher than the frozen (26.2%) and that of the surgical (35.0%) was slightly higher than the nonsurgical (30.8%).
