Evaluation of equilibration time on boar semen cryopreservation protocols: a physiological and morphofunctional study

Seminal cryopreservation is considered as a technique of broad applicability and efficiency for determinate production systems, which optimizes productivity and animal genetic improvement. However, its use within the swine industry is absent due to the singularities of the sperm of this species. Thus, several studies are searching for alternatives that improve the post-thawing performance of boar spermatozoa, where one option that has been gaining ground in research focused on boar andrology is the application of equilibration time (ET) to protocols of cryopreservation. Equilibration time is nothing more than the period at which spermatozoa are kept in contact with the extender components at a temperature of 5ºC to ensure an osmotic balance between the intra and extracellular environment. In this context, the present study aimed to validate the ideal period of ET, aiming at the best post-thawing results of boar semen, besides verifying its effects on the physiological and morphofunctional characteristics of these cells. For the first time, the effects of ET were described and showed the importance of the particular freezing characteristics of boar ejaculates and the evaluated sperm parameters. Where, the post-thawing sperm motility of ejaculates considered as good freezers (GFE) was better when maintained after 2 hours of ET, and the plasma and acrosomal membrane integrity were higher when in poor freezer ejaculates (PEF) are exposed to the same ET. It was also observed that a prolonged 4 h ET was detrimental to both ejaculates and that 2 h ET showed no detrimental effects on any sperm parameter. Therefore, we can conclude that the application of 2 h ET to the end of the cooling curves during the boar sperm cryopreservation has beneficial effects on the post-thawing cell morphophysiology. (AU)