Hypo-osmotic swelling of dog spermatozoa

Dog spermatozoa were evaluated for their ability to swell when exposed to hypo-osmotic conditions. A medium was developed to allow spermatozoal swelling to be identified easily; both the number of swollen spermatozoa and their morphological appearance were influenced by the characteristics of this medium. The number of swollen spermatozoa was inversely proportional to the number of dead spermatozoa in a sample. Although spermatozoal swelling was highly repeatable there was no correlation with spermatozoal motility, morphology or vital staining. Electron microscopic studies demonstrated that swelling of spermatozoa was characterized by ballooning of the tail membrane and internal flexion of the axial filaments. Spermatozoa with damaged membranes were unable to swell. Hypo-osmotic swelling of dog spermatozoa is reliable and repeatable and may be a useful assay for the diagnosis of spermatozoal membrane function.