Effect of different freezing velocities on the quality and fertilising ability of cryopreserved rabbit spermatozoa

The freezing step of the cryopreservation protocol negatively influences the quality and fertilising ability of rabbit spermatozoa. This study determines the effect of different rates of freezing on the quality and fertilising ability of rabbit spermatozoa cryopreserved with dimethylsulfoxide (DMSO) (1.75M) and sucrose (0.05M). Ejaculates from meat rabbit line males (n ¼12) were pooled and each pool (n ¼7) was split into four aliquots. One group of straws (control, C) was frozen in static liquid nitrogen vapour (5cm above the liquid nitrogen, 10min) and the other groups were frozenatdifferentfreezingrates(8Cmin � 1 )from � 68Cto� 1008Cusingaprogrammablefreezer:slow(� 158Cmin � 1 ,S), medium (� 408Cmin � 1 , M) or fast (� 608Cmin � 1 , F). After thawing (508C, 12s), the quality was highest (Po0.05) in C and M samples and lowest in S and F samples. F samples presented the lowest litter sizes (P#0.05) and fertility whilst M samples exhibited the highest values. In conclusion, the freezing rate affects both the quality and the fertilising ability of frozen-thawed rabbit spermatozoa, with both slow (� 158Cmin � 1 ) and fast (� 608Cmin � 1 ) freezing rates being detrimental for the quality and fertilising ability. Additional keywords: cryopreservation, freezing-thawing, programmable freezer, semen. Received 9 January 2014, accepted 9 February 2014, published online 21 February 2014