RESUMO
This study aimed to assess the suitability of egg yolk (EY) supplementation to a tris-citric acid-based extender on cryosurvival of guinea pig (Cavia porcellus) epididymal spermatozoa. Two synthetic-based extenders, tris-citric acid-glucose plus 20% EY (TCG-EY) and tris-citric acid-fructose (TCF) both with 5% glycerol, were compared. Thirty-two epididymides were recovered from 16 adult guinea pig males by gonadectomy, and then the sperm samples were retrieved by retrograde flushing using TCG-EY and TCF extenders for left or right epididymis, respectively. TCG-EY and TCF sperm samples were frozen in static liquid nitrogen vapors through a two-step cooling procedure. Before freezing, the percentage of progressive sperm motility and sperm with intact plasma and acrosome membranes from TCG-EY sperm samples were higher (p < 0.05) than those diluted with TCF. Post-thaw sperm kinematic variables and membrane integrity were drastically reduced (p < 0.001) compared with prefreezing samples, regardless of extender type. The post-thaw plasmatic and acrosome membrane integrity from TCG-EY sperm samples was higher (p < 0.05) than those from TCF samples. Except for the length, the morphometric head dimensions of sperm diluted with TCG-EY or TCF did not vary (p > 0.05) after the freezing-thawing process compared with the prefreezing samples. In conclusion, despite greater cell cryoinjury with both extenders, the EY supplementation exerted greater cell membrane protection before and after the freezing-thawing process. This research shows an in-depth analysis of guinea pig sperm cryopreservation; however, more studies are recommended.
