Sperm fractionation and storage

Claim 1

A process for reducing the motile sperm losses resulting from the storage of motile-sperm containing semen in a frozen state prior to use for artificial insemination purposes, which comprises (a) separating the motile sperm from the other components of the semen prior to freezing by (i) maintaining at least the sperm portion of the semen, as such or suspended in an aqueous suspending vehicle which is physiologically acceptable to the sperm and which does not substantially retard the downward migration rate of motile sperm, as an upper layer in interfacial contact, at a temperature at which the motile sperm are motile, with a lower discrete layer of an aqueous contacting medium which is physiologically acceptable to the sperm and in which the motile sperm migrate downwardly at a slower rate than in the upper layer, until at least a portion of the motile sperm of the separated sperm have migrated downwardly into the contacting medium, thereby producing a sperm fraction having a higher proportion of motile sperm than in the starting sperm, and (ii) thereafter separating the contacting medium, containing the motile sperm enhanced fraction of the starting sperm, from the upper layer; and (b) storing the separated motile sperm fraction in a frozen state.