Abstract

Bisected embryos not only create identical twins, but can also improve the efficiency of embryo transfer. We report here our experiences in applying the technique to sheep MOET programmes. Our basic technique involves holding a Day 5-6 embryo by negative pressure on a holding pipette and tearing the zona pellucida using 2 needles. A razor blade fragment is used to bisect the embryo and if required, a suction pipette manipulates demi-embryos into suitably prepared host zonae. In a preliminary study bisected embryos were examined for development during 24-48 h culture. Bisection in Ca2+, Mg2+-free media had no effect on viability. Naked demi-embryos blastulated more readily than those which were zona-enclosed and later stages tended to be the most viable, with morulae showing particularly poor development. This was supported by transfer data, where 11% of bisected late morulae, 50% of early blastocysts and 74% of blastocysts resulted in lambs. In comparison, 40% of control (unbisected) embryos lambed. Transfer of zona-enclosed demi-embryos tended to yield more lambs per original embryo (67%) than naked demi-embryos (43%). When the technique was applied to early blastocysts and blastocysts during 3 exotic sheep multiplication programmes in 1988, 47% and 55%, 100% and 39%, 73% and 47% of bisected and control embryos resulted in lambs respectively. Survival to lambing of dehydrated late morulae, bisected and subsequently enclosed in zonae, was similar to untreated control embryos (73% VS 59%) and greater than for naked embryos (36%). Our experiences indicate that bisected early blastocysts and blastocysts can increase the number of offspring in a MOET programme. However, since few blastocysts are available for bisection, and survival of demi- embryos is variable, we do not routinely use the technique.

RD, Wallace

Proceedings of the New Zealand Society of Animal Production, Volume 50, , 393-396, 1990