In cattle less than 10% of the embryos develop to the blastocyst stage when embryos are cultured individually, however when bovine embryos are cultured in groups a typical 25-35% of blastocysts can be observed. This tendency, i.e. improved embryo development in group culture, has also been demonstrated in other mammalian species, such as mouse, cat and human. The main reason for this beneficial outcome of group culture has been ascribed to the presence of autocrine factors, which are factors secreted by preimplantation embryos that act upon the embryo itself or the neighboring embryos .