Spermatozoa “swim” from the vagina or cervix (depending on species) to the site of fertilization (oviduct) and are in contact with uterine fluid (UF) during their passage through the uterus, and then, when they are near to the oocyte, they are in contact with oviductal fluid (OF).

This system of sperm capacitation, which uses OF and/or UF as protein additives, does not require centrifugation, which means major benefits in reducing the stress to which male gametes are subjected during the process of seminal plasma separation. This helps to select those sperm with better quality and DNA integrity.