Bovine embryos are routinely produced in goups of 25 because of the improved embryo development in such setting. The superiority of the system is probably caused by the secretion of embryonic paracrine factors, which are positively influencing neighbouring embryos. In part 1 we will investage differential secretion between good (fast) and bad (slow) embryos. Next this model will be used in a human preclinical and clinical study.