Evaluation of two extenders in Canine epididymal spermatozoa freezing (Polyvinyl alcohol and egg yolk)

Egg yolk (EY) is a common component of semen extenders due to its effectiveness in protecting the sperm membrane from cold shock during cryopreservation and it is also rich in proteins, vitamins, antioxidants, and phospholipids. However, the EY is an undefined component and at the same time dangerous due to the risk of transmission of pathogenic agents. For this reason, it is necessary to evaluate the use of other components that reduce this problem. An understudied alternative is polyvinyl alcohol (PVA). For this reason, this investigation evaluated the effect of PVA and EY supplemented with TCG diluent (tris, citric acid, glucose) on the cryosurvival of dog epididymal spermatozoa (ES). For this, ES were recovered using the retrograde flow technique in 15 orchiectomized adult dogs to form five pools (4-6 epididymal samples/pool). Each pooled sample was divided into two aliquots, which were subsequently diluted and frozen using two additives supplemented to the TCG diluent: 1% (w/v) PVA [TCG– PVA] and 20% (v/v) egg yolk [TCG–EY]. After thawing, morphological abnormalities, vitality (eosin/nigrosin), plasma membrane integrity (propion iodide), and kinematic variables (CASA system, SCA-2018®) were analyzed. The results demonstrated that the vitality and integrity of the plasma membrane were superior (P<0.05) in samples frozen with TCG–EY, compared to those samples frozen with TCG–PVA. Likewise, the samples frozen with TCG–EY obtained higher post-thaw values (P<0.05) of kinematic variables such as total and progressive motility, average and rectilinear velocities, straightness index and flagellum beat frequency, compared to with frozen samples with TCG–PVA. In conclusion, enhancement of EY to TCG medium was effective in freezing dog ES, as it improved vitality, plasma membrane body, and sperm kinetics; however, the addition of 1% PVA did not improve the response to cryopreservation.