Colloid centrifugation can be used to separate heterogeneous populations of cells particularly semen samples, which typically contain mixtures of spermatozoa at different stage of maturity together with dead and dying spermatozoa and also non-sperm cells. Colloids can be used to enrich the population of spermatozoa that are viable and functional; these are the spermatozoa that are needed for fertilization in Assisted Reproduction. Sperm samples obtained after colloid centrifugation may be enriched for motile, morphologically normal spermatozoa with intact chromatin. Insemination of mares with stallion sperm samples prepared by colloid centrifugation resulted in a higher pregnancy rate per cycle than controls, confirming that the good sperm attributes observed in the laboratory were indicative of functional spermatozoa. The method does not simply enrich for viable spermatozoa by inhibiting dead or dying spermatozoa from passing through the colloid since emerging evidence shows that colloid centrifugation can select for spermatozoa with certain properties such as metabolic activity. Other reproductive cells, such as spermatids or progenitor cells, may also be purified by colloid centrifugation. This review describes the history of colloid centrifugation for selecting spermatozoa, compares colloid centrifugation with alternative techniques, and finally describes some of the applications of the technique within the animal breeding industry.

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