Increasing Extender Viscosity Improves the Quality of Cooled Boar Semen

The use of several types of gelling extenders for the storage of semen from several domestic species in the solid state has been shown to have beneficial effects on some semen quality parameters. The objective of this study was to evaluate the effect of a new high-viscosity semen extender, Zoosperm ND-5 3D® (Import-Vet, Centelles, Spain), on the the quality of boar spermatozoa at preserved at 17ºC for 7 days. Sodium alginate was used for the first time to increase the viscosity of the extender for the liquid storage of boar semen. The same extender, but without increased viscosity, was used as a control extender (Zoosperm ND-5®, Import-Vet, Centelles, Spain). Sixteen ejaculates from four Pietrain boars were evaluated for motility (by the CASA system), and for viability, acrosome status, plasma membrane fluidity, externalization of phosphatidylserine at the plasma membrane of the spermatozoa and mitochondrial membrane potential (by flow cytometry). In samples diluted with the Zoosperm ND-5 3D® viscous extender, the STR (straightness) parameter and the number of progressively motile spermatozoa were higher compared to those of the non-viscous extender (p < 0.05). In addition, the number of spermatozoa with damaged acrosomes, an unstable sperm plasma membrane and externalization of phosphatidylserine at the plasma membrane was lower in samples treated with the viscous extender (p < 0.05). In conclusion, an increase in extender viscosity improves quality of boar spermatozoa following long-term storage.