Computer assisted sperm morphometry in mammals: A review

•A complete description of the CASMA technique, including recent developments, is provided.•The effect of different factors affecting sperm morphometry is discussed.•The results of sperm morphometry in the different species are reviewed and discussed.•Possible applications of sperm morphometry are critically exposed. Computer-assisted sperm morphometry analysis (CASMA or ASMA) systems were developed to reduce the subjectivity of sperm morphology assessement. This review focuses on a complete description of the CASMA technique, including recent developments, factors of variation, results in the different species and possible applications. Techniques to study sperm morphometry include light microscopy, phase-contrast microscopy and, more recently, fluorescence microscopy. Most published studies on sperm morphometry have been centered on the whole sperm heads, although some of them also measured other parts of the sperm structure, such as the nucleus, acrosome, midpiece or flagellum. The independent study of sperm components may be more informative than the traditional assessment of the whole sperm head. Morphometric data provided by the CASMA system may be analyzed using classical statistics although, given the heterogeneity of spermatozoa in the ejaculates, the study of sperm subpopulations using clustering procedures may be more informative. Morphometric results may vary depending on factors intrinsic and extrinsic to the semen donor. Intrinsic factors may include, among others, genetic factors, age and sexual maturity. Extrinsic factors may include those related to the influence of environment on the donor, as well as those related with sample processing and the morphometric analysis itself. Once standardized, this technique may provide relevant information in studies focused on evolutionary biology, sperm formation, sperm quality assessment, including prediction of the potential fertility, semen cryopreservation, or the effect of reprotoxicants.