Assessing the quality of raw semen: a review.

An analysis of semen characteristics can provide a reasonable basis upon which to develop a strategy for maximizing the fertility of a stallion. However, the repeatability of semen characteristics between ejaculates within stallions is low to moderate. Factors such as season, collection technique, frequency of collection and disturbances in spermatogenesis contribute to this variation. Fertility can, however, be influenced by a host of other factors besides semen characteristics, including management, semen handling procedures and the number of mares being bred. Parameters usually included in a conventional evaluation of raw semen quality are volume, sperm concentration, total number of spermatozoa in the ejaculate, percentages of motile spermatozoa, sperm morphology, seminal pH, longevity of sperm motility and bacteriological status. Although, these evaluations provide a lot of information, their correlations with fertility are somewhat conflicting. However, it seems likely that the prediction of male fertility could be improved if additional parameters based on the functional characteristics of spermatozoa were to be used. Several functional tests have been investigated, such as the use of fluorescent stains as a marker for cell membrane integrity, sperm-oocyte binding tests and the hypoosmotic swelling test. In this study, emphasis is placed on sperm motility and sperm morphology, but in addition, some functional tests are also discussed.