The present invention provides a new and improved sperm stimulating additive comprising a certain amount of inorganic pyrophosphate (PPi). Addition of PPi in the media for human/animal in vitro fertilization (IVF) improves fertilization rate; addition of PPi in the semen extender for farm animal artificial insemination (AI) may improve pregnancy rates; furthermore, mammalian oocytes matured in vitro in a medium including PPi attain improved fertilization and developmental potential, while embryos cultured in medium supplemented with PPi have improved development to blastocyst.