Sperm cell processing methods

A method of processing animal sperm cells comprising the steps of:

• collecting sperm cells from a male animal;
• sorting the sperm cells to obtain a quantity of sperm cells having a desired characteristic, said quantity of sorted sperm cells being contained in a first volume of fluid having a first concentration of sperm cells therein;
• subjecting the sperm cells to a concentration step in which the concentration of said sperm cells is increased to a second concentration greater than said first concentration, wherein said concentration step comprises flowing at least a portion of the first volume of fluid through a first filter at a pressure differential across the first filter of less than about 20 in. mercury, said filter having filter pores sufficiently small to inhibit passage of said sperm cells there through, and retaining a second volume of concentrated fluid containing said sperm cells in a container;
• flowing at least a portion of said second volume of concentrated fluid through a second filter having filter pores sufficiently small to inhibit passage of said sperm cells there through, retaining a third volume of concentrated fluid containing said sperm cells in the container;
• and
• flushing said second filter with a resuspension fluid to remove sperm cells from the second filter for addition to said third volume to arrive at said second concentration.