The mean total cell number in our SCNT blastocysts is now also comparable with IVF-produced embryos. Even though early embryo transfer has been successful in producing live piglets, it has a major disadvantage in that the quality of the SCNT embryos cannot be determined prospectively (they are all either zygote- or two-cell stage appearing). An excessive number of embryos transferred to surrogates can actually reduce the number of piglets born, as the embryos may become too crowded and, as they compete for resources, the less developed embryos die.