Periimplantation-like growth and development of mouse blastocysts in medium containing horse serum.

Horse serum (HS) supported growth and differentiation of blastocysts as well as or better than fetal bovine serum (FBS) (p less than 0.01) as measured by a) the onset of trophoblastic outgrowth, b) the size of the resultant outgrowths, c) the size of nuclei in trophoblasts after their outgrowth and d) the size of the inner cell mass in outgrowths. Moreover, polyamines were found to be approximately 10-100 times less toxic to embryos when added to medium containing HS than when the medium contained FBS.