The ultimate goal of evaluating frozen semen is to predict the fertilizing capacity. Making decision concerning the use of a stud dog for mating or artificial insemination or for semen cryopreservation will depend on certain parameters indicative of semen quality. The fertility of semen samples with very high or very low quality may be relatively predictable, but it is more difficult for semen samples of medium quality, as there is no single sperm attribute is highly and accurately correlated with fertility in-vivo.