High cooling rate of 60°C/min around ice nucleation during cryopreservation compromises chicken sperm viability

The present study compares two protocols for the cryopreservation of chicken semen. Both protocols had an initial low cooling rate in the first step, followed by higher cooling rates around ice nucleation (Protocol 1) or following the dissipation of the latent heat of fusion (Protocol 2) in the second step. Semen ejaculates obtained from 12 roosters were diluted with Rootex with 6% dimethylformamide and frozen following either Protocol 1 (from +5°C to -10°C at 5°C/min and from -10°C to -130°C at 60°C/min) or Protocol 2 (from +5°C to -35°C at 7°C/min and from -35°C to -140°C at 60°C/min). Compared with fresh semen, following both protocols, cryopreservation resulted in reduced post-thaw sperm quality (p < .001). Post-thaw percentage of sperm with an intact plasma membrane was greater using Protocol 2 than Protocol 1 (p < .05). The results suggest that high cooling rates around the time of ice nucleation are not recommendable.