Influence of the Embryo and Uterus on Luteal Function in the Sheep

THE transfer of sheep eggs to recipient ewes is a well-established experimental procedure. Using the method developed by Hunter, Adams and Rowson1 successful transfers of eggs and blastocysts have been performed during the first 8 days of the 16-day cycle1–4. No transfers have yet been reported after that stage. Recently, we found that with the use of the standard technique1 pregnancy will result from the transfer of blastocysts to recipient ewes up to the eleventh day after œstrus. However, more advanced embryos cannot be transferred by that technique owing to the rapid growth of extra-embryonic membranes after the eleventh day of pregnancy. A modified method of recovering and transferring 12, 13 and 14 day embryos has now been developed. It is the purpose of this communication to describe in brief both that technique and its application in our study of the mechanisms that regulate luteal function in the sheep.