Effect of freezing extender composition and male line on semen traits and reproductive performance in rabbits

This study was conducted to elucidate the effect of different freezing extenders on two lines selected for hyperprolificacy and longevity (H and LP, respectively). In extender A, dimethyl sulphoxide (Me2SO) and sucrose were used as cryoprotectants. In extenders B and C, the sucrose was replaced by 20% egg yolk, and in extender C the Me2SO was substituted by acetamide. Semen was packaged in 0.25 ml plastic straws and cooled at 5°C for 45 min, and then was frozen in liquid nitrogen vapour for 10 min before being plunged into the liquid nitrogen. Thawing was carried out by immersing the straws in a water bath at 50°C for 10 s. Frozen-thawed semen characteristics and reproductive parameters were affected by freezing. Extender C showed significantly lower post-thawing quality traits than any of the three extenders. Acrosome integrity was significantly improved when Me2SO was used as cryoprotectant. Sucrose replacement by 20% egg yolk had no effect on acrosome integrity but provided significantly lower sperm motility and viability. Freezing extender affected fertility rate, total born, number of implantation sites and gestational losses, obtaining better results when extender A was used. The acrosomal integrity after frozen-thawed process showed a significant correlation with fertility at 12th day and also at birth, indicating that an increase in acrosomal integrity leads to an increase in both fertilities (12th day and at birth). A positive correlation between motility of semen and implantation sites was found. The post-thawing quality traits of semen were not affected by the genetic line, although LP line showed higher total born and lower foetal and gestational losses. The findings of this study suggest that freezing extender composition has a significant effect on the success of rabbit sperm for preservation, and when Me2SO was used as permeable cryoprotectant sucrose provided better protection compared with egg yolk and improved reproductive traits, and, on the other hand, the male genotypes used in the present study had no effect on frozen-thawed sperm parameters but negatively affected some of the reproductive parameters.