Effect of cryoprotectants and thawing temperatures on chicken sperm quality

There is need for standardization of freezing–thawing protocol for rooster semen to minimize variability among results. Therefore, we aimed to compare effect of four different permeating cryoprotectants and two thawing temperatures (37 vs. 5°C) on sperm post-thaw motility and to analyse combined effect of the best permeating cryoprotectant (P-CPA) with one of four non-permeating cryoprotectants (N-CPA) on post-thaw quality of rooster semen evaluated in vitro. Pooled semen from Ross PM3 rooster heavy line was diluted in Kobidil extender and frozen in cryoprotectant solution containing 6% dimethylacetamide, 7.5% dimethylformamide, 9% N-methylacetamide or 8% ethylene glycol (EG) in liquid nitrogen vapours. To determine the best thawing rate, straws were thawed either at 37 or 5°C. Furthermore, samples were frozen in the presence of the best N-CPA either with 0.75 mol/L ficoll, 0.2 mol/L sucrose, 0.2 mol/L trehalose or 0.05 mol/L glycine. Sperm motility, membrane destabilization and viability were analysed to compare different freezing–thawing conditions. In addition, morphology and ultrastructure analysis were performed to compare fresh and frozen-thawed sperm quality. Our results indicate that the combination of EG and the thawing at 5°C improves (p ≤ .05) sperm post-thaw motility. Moreover, ficoll addition to EG-based freezing extender provided additional beneficial effect (p ≤ .05) on progressive movement and apoptosis incidence. Further work should evaluate different N-CPA concentrations to improve freezing protocol. In addition, fertility evaluation and testing on different chicken lines are needed in order to contribute to animal genetic resources bank.