Method of increasing the economic value of breeding stock semen

A method of artificially inseminating a plurality of animals with aliquots of semen from a breeding stock individual of the species, each of which contains a population of motile sperm large enough to ensure successful artificial insemination therewith, which comprises the steps of:

• (a) fractionating the collected semen into a first fraction from which the immotile sperm and non-sperm components have been separated, containing from about 10% to about 80% of the motile sperm of the semen, suspended in a liquid vehicle which is physiologically acceptable to the sperm and for artificial insemination, and into a second fraction, containing the remainder of the motile sperm thereof, also suspended in a liquid vehicle which is physiologically acceptable to the sperm and for artificial insemination by the steps of (i) maintaining at least the sperm portion of progressively motile sperm-containing semen, either as such or suspended in an aqueous suspending vehicle physiologically acceptable to the sperm, as an upper layer in vertical interfacial contact, at a temperature at which the motile sperm are motile, with a lower discrete layer of a first aqueous contacting medium physiologically acceptable to the sperm in that the motile sperm migrate downwardly at a slower rate than in the upper layer, until a portion only of the motile sperm of the semen having migrated downwardly into the contacting medium, thereby producing a contacting medium containing a higher proportion of Y to X sperm than in the starting sperm, thereby producing in said upper laer a first portion of the second fraction of sperm and (ii) repeating the step at least once, employing in the upper layer the motile sperm which have migrated to the first aqueous contacting medium and as the lower layer a second aqueous contacting medium physiologically acceptable to the sperm and in which the motile sperm migrate downwardly at a slower rate than in the first contacting medium, thereby producing in the lower layer the first fraction of sperm, and in the upper layer a second portion of the second fraction of sperm;
• (b) dividing the first fraction of sperm into a plurality of aliquots, each of which contain a population of motile sperm largel enough to ensure a pregnancy when used for an artificial insemination;
• (c) dividing the second fractions of sperm into a plurality of aliquots, each of which contain a population of motile sperm large enough to ensure a pregnancy when used for an artificial insemination;
• (d) artificially inseminating a plurality of individuals of that species in which a predominance of male off-spring is desired with the aliquots of the first fraction of sperm;
• and
• (e) artificially inseminating a plurality of individuals of that species in which a predominance of male off-spring is not a desired objective with the aliquots of the second fraction of sperm.