Milk supplements in a glycerol free trehalose freezing extender enhanced cryosurvival of boar spermatozoa

Objective: To evaluate the effect of skim milk and/or coconut milk in a glycerol-free trehalose extender to improve cryosurvival of boar spermatozoa.Methods: Sperm samples were diluted in an egg-yolk-based freezing extender containing 100 mM trehalose and 0.25% Equex STM supplemented with coconut milk or/and skim milk at 2% or 5% (w/v). Spermatozoa were cryopreserved in 0.5 mL straws and thawed by a rapid transient method (at 70 °C for 8 s) followed with a stabilizing procedure at 39 °C. Thawed samples were analyzed for motility, viability, high mitochondrial membrane potential (HMMP), and acrosome damage.Results: Even on the presence of egg yolk, motility, HMMP and viability were significantly higher in extender supplemented with 2% skim milk than controls without skim milk (P < 0.05). Post-thaw viability significantly improved with the addition of 2% skim milk plus 2% coconut milk as well (P < 0.05). Acrosome damage was considerably lower when the extender was supplemented with 2% coconut milk (P < 0.05), whereas the benefit was masked in the presence of 2% skim milk.Conclusion: 2% skim milk can be used as supplements for a glycerol-free trehalose and egg yolk-based extender to improve post-thaw survival of boar spermatozoa, whereas 2% coconut milk has an effect to protect boar spermatozoa from acrosome damage