Flow cytometric determination of the sperm cell number in diluted bull semen samples by DNA staining method.

Flow cytometric determination of the number of bull sperm cells showed that the number of spermatozoa measured by light scattering may considerably differ from the actual number of sperm cells in the samples, depending on the proportion of contaminating particles, similar in size to sperm cells. No accurate information can be obtained from the sum of live and dead cells distinguished by means of double fluorescence staining, since a part of the sperm cell population is in a transitory state i.e. between the viable and dead states, so it cannot be stained by either dye. The number of spermatozoa in the sample can be determined very accurately if the sample is treated first with Nonidet-P-40 detergent then stained with propidium iodide. With this procedure the DNA content of each cell nucleus can be labeled and, through detecting the fluorescence signals, the actual sperm cell count of the sample can be determined with the accuracy of 95-98%.