Attempted production of monozygotic twins in sheep by bisection of blastocysts

Abstract

Various techniques have been described for the production of monozygotic twins in sheep by bisection of embryos and these will be reviewed. The present study utilised a simple procedure with an inexperienced operator on ovine late morulae/expanded blastocysts which were collected surgically by flushing uteri of donor ewes between 7 and 7•5 days post coitus. The technique for bisection involved use of a tungsten wire microneedle to split the embryo into two pieces once it had been immobilised on the tip of a microsuction pipette. Each naked demi-embryo produced in this manner possessed part of the trophectoderm and inner cell mass from the original embryo. Of 13 blastocysts that were bisected, nine appeared to be split into approximately equal halves. However, all 26 demi-embryos were transferred by a laparoscopic procedure to uteri of synchronised (± 12 hours) recipient ewes; one monozygotic pair per recipient. Based on non-returns to oestrus and a real-time ultrasonic scan, five (i.e. 38%) of the recipients were confirmed as pregnant between days 50 and 80 of gestation. However, one of these ewes failed to carry a conceptus to term and the other four remaining ewes all produced single lambs (15% embryonic survival). Although this study failed in its primary objective, the results demonstrate that ovine blastocysts have the ability to maintain their development following a substantial reduction in cellular mass. The bisection procedure used is still considered to have potential for producing monozygotic twin lambs for physiological or nutritional studies.