DONOR AND RECIPIENT EWE FACTORS AFFECTING IN-VITRO DEVELOPMENT AND POSTTRANSFER SURVIVAL OF CULTURED SHEEP EMBRYOS

Donor and recipient factors were assessed during development of embryo s following superovulation, collection at the pronuclear and two-cell stage, culture in Synthetic Oviduct Fluid medium for 5 days and twin t ransfer into synchronised recipients to elucidate what factors affect embryo development and post-transfer survival. In particular, the admi nistration of exogenous progesterone to recipients using an intravagin al CIDR(TM) device immediately following embryo transfer was investiga ted. From 138 embryos collected from 30 donor ewes, 75% (103) were of transferable quality following culture, of which 100 were transferred to 50 recipients. There was significant variation (P < 0.001) in embry o development to the blastocyst stage between different donor ewes, bu t this was not related to the donor ovulation rate. At ultrasound sono graphy (approximately Day 60 of pregnancy), 58% of recipients were pre gnant and 42% embryos had survived. Donor ovulation rate was related t o embryo survival (P < 0.05) after transfer; the survival rate of embr yos from ewes with high ovulation rates was lower than that of embryos from ewes with low ovulation rates. Exogenous progesterone supplement ation following transfer did not affect embryo survival, rate of embry o development or plasma progesterone levels. In general, the results f rom this study suggest that factors other than efficacy of embryo cult ure can affect the outcome of embryo survival following transfer and t hat, where possible, these factors should be considered and balanced i n experimental designs.