Motility is an essential characteristic of all fl agellated spermatozoa and assessment of this parameter
is one criterion for most semen or sperm evaluations. Computer-aided sperm analysis (CASA)
can be used to measure sperm motility more objectively and accurately than manual methods,
provided that analysis techniques are standardized. Previous studies have shown that evaluation
of sperm subpopulations is more important than analyzing the total motile sperm population
alone. We developed a quantitative method to determine cut-off values for swimming speed to
identify three sperm subpopulations. We used the Sperm Class Analyzer ® (SCA) CASA system
to assess the total percentage of motile spermatozoa in a sperm preparation as well as the
percentages of rapid, medium and slow swimming spermatozoa for six mammalian species.
Curvilinear velocity (VCL) cut-off values were adjusted manually for each species to include 80%
rapid, 15% medium and 5% slow swimming spermatozoa. Our results indicate that the same VCL
intervals cannot be used for all species to classify spermatozoa according to swimming speed.
After VCL intervals were adjusted for each species, three unique sperm subpopulations could be
identifi ed. The effects of medical treatments on sperm motility become apparent in changes in
the distribution of spermatozoa among the three swimming speed classes.