Commercial application of flow cytometry for evaluating bull sperm

Artificial insemination using semen from genetically superior sires remains one of the most effective biotechnologies ever commercialized for animal breeding purposes. Genetic progress, however, cannot begin until conception occurs. Processing laboratories that provide cryopreserved bull semen for commercial use depend on in vitro assays of semen quality to identify samples that are expected to result in less than desirable conception rates. These identified samples are discarded, rather than released to salable inventories, with the desired effect of minimizing variance in field fertility among both sires and individual collections. Although the industry was successfully founded on subjective assessment of motility and acrosome integrity, flow cytometric and computer-assisted sperm analysis offer more objective and repeatable measures of sperm quality attributes. Albeit more expensive to implement, the increased precision and repeatability when using these objective assays lends to greater confidence in the accuracy of decisions for individual collections and (or) bulls. The efficacy of a quality control program is evidenced by the range in sire fertility estimates calculated from field fertility data, which have historically indicated >90% of all sires achieve fertility deviation within ±3% points of the breed average. This impressive precedent implies somewhat limited opportunity for transition to objective assessments to have a meaningful impact on an already narrow range of fertility distributions. Nonetheless, flow cytometric assessments of novel attributes of sperm quality hold promise for detection of truly sub-fertile sires (deviations < -3) that presently elude detection with use of existing semen bioassays.