Background: One-cell mouse embryos were used to determine the effects of drop size and number of embryos per drop for optimum development in vitro. Methods: Embryos were collected from immature C57BL6 female mice superovulated with pregnant mare serum gonadotropin and human chorionic gonadotropin and mated by CD1 males. Groups of 1, 5, 10, or 20 embryos were cultured in 5-, 10-, 20-, or 40-mul drops of CZB under silicon oil at 37.5-degrees-C in a humidified atmosphere of 5% CO2 and 95% air. Results: Development score for embryos cultured in 10 mul was higher than that of embryos cultured in 20 or 40 mul. Embryos cultured in groups of 5, 10, or 20 had higher development scores than embryos cultured singly. The highest development score was obtained by the combination of 5 embryos per 10-mul drop. The percentage of live embryos in 20 or 40 mul was lower than that of embryos cultured in 10 mul. Additionally, the percentage of live embryos cultured singly was lower than that of embryos cultured in groups. Conclusions: Our results suggest that a stimulatory interaction occurs among embryos possibly exerted through the secretion of growth factors. This effect can be diluted if the embryos are cultured in large drops or singly.
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