The general perception on transferring SCNT embryos into surrogates is that SCNT embryos should be transferred as early as possible to minimize potential damage to the embryos from the in vitro environment. Thus, unlike in other species, such as cattle and sheep, embryo transfer
of SCNT pig embryos is typically conducted at an early stage. The quality of SCNT embryos and the average litter sizes of clones have increased over time; our records of over 670 live births show that the largest litter size was 11 piglets (unpublished data). Also, there have been significant improvements in the culture of SCNT embryos; depending on the donor cells, typically an average of 20–40% of fused embryos become blastocysts (unpublishedobservation).