Factors affecting the survival of bisected sheep embryos in vivo

Two experiments were carried out to examine the effects of different factors on the survival of split sheep embryos. In Experiment 1, embryos collected on Day-6, Day-7 or Day-8 were bisected and transferred into recipient ewes in pairs. The proportions of Day-6, Day-7 and Day-8 demi-embryos developing to lambs were 26% (14/54), 30% (31/102) and 32% (24/74), respectively. Replacement of bisected late morula to expanded late blastocyst stage embryos into zonae did not affect their survival rate (P>0.5). The proportion of demi-embryos developing to lambs in recipients with two or more ovulations was higher (35%, 53/152) than in recipients with a single ovulation (21%, 16/78 ; P<0.05). In Experiment 2, Day-6 embryos were split with or without exposure to 0.25 M of sucrose and were transferred into recipients in pairs or singly. Exposure to 0.25 M of sucrose decreased the proportion of split embryos developing to lambs compared with that of the controls (31%, 22/70 vs 49%, 34/70 ; P<0.05). The effects of the number of demi-embryos transferred or the stage of development on the survival rate were not significant (P>0.05). The number of lambs born per original embryo was the highest when the embryos were split without exposure to sucrose and transferred into recipients singly (106%, 17/16).