During cryopreservation, both
physical and chemical factors including the rapid change in
temperature or thermal stress, oxidative stress and osmotic
stress lead to the damage of the sperm plasma membrane
[19]. In general, the egg yolk-based freezing extender of
boar semen consists of cryoprotectant, sugar, buffer and
antibiotic [16]. Glycerol is the most common cryoprotectant
used in the egg yolk-based semen extender for cryopreservation
of the boar semen [14] and egg yolk is regarded
as a non-permeable cryoprotectant.