Characteristics of spermatozoa of whole ejaculate and sperm-rich fraction of dog semen following exposure to media varying in osmolality.

This study aimed to analyze the effects of different osmolalities on the characteristics of spermatozoa originating from whole ejaculates (WE; including the prostatic fluid) and the sperm-rich fractions (SRF). Ejaculates, collected from four mixed-breed dogs, were exposed for 10 min at room temperature to Tris-fructose-citrate (TFC) solution with osmolality ranging from 150 to 1100 mOsm. After treatment spermatozoa were evaluated by microscopic analysis of motility and fluorescent assessments of plasma membrane integrity (carboxyfluorescein diacetate and propidium iodide, CFDA/PI) and mitochondrial function (rhodamine 123, R123). Irrespective of the sperm source, there was a complete loss of motility when spermatozoa were exposed to TFC solution with 1100 mOsm. There were no marked differences in the sperm characteristics between media with 300 and 350 mOsm, regardless of the ejaculate collection procedure. However, a marked reduction in motility of spermatozoa retrieved either from the WE or SRF was observed after exposure to different anisosmotic conditions (150, 550 and 800 mOsm). In all dogs, spermatozoa from the WE exhibited greater osmotolerance in terms of plasma membrane integrity and mitochondrial function when exposed to anisosmotic conditions (150, 550, 800 and 1100 mOsm). There were inter-dog variations in response to various osmotic conditions. The findings of this study indicated that spermatozoa from the WE tolerated exposure to a wider range of osmolality than those from the SRF. It seemed that the presence of prostatic fluid of dog semen rendered the sperm membrane structures less susceptible to osmotic stress.