Freezing stallion semen with the new Cáceres extender improves post thaw sperm quality and diminishes stallion-to-stallion variability

Ejaculates from 7 stallions were split and simultaneously frozen in three different extenders, INRA 96 egg yolk glycerol, Ghent and the newly developed extender Caceres. After thawing, samples were evaluated for motility (CASA system) sperm membrane integrity and early membrane changes (YoPro-1/Eth staining), acrosome integrity (FICT-PNA), and mitochondrial membrane potential (JC-1) (flow cytometry). Samples frozen in Caceres extender consistently showed the best results in post-thaw motility (increases ranging from 11 to 17%, p < 0.05) and velocity (p < 0.05), membrane integrity (increases ranging from 11 to 14%, p < 0.05) and mitochondrial membrane potential (p < 0.05). It is concluded that this new extender should be included in a freezeability test to determine the best extender for each individual.