Effect of extender on the quality and incubation resilience of cryopreserved Holstein bull semen

There are still concerns over sperm quality when plant-based diluents are used instead of animal-based semen extenders. Therefore, in our study we compared the effects of one soybean lecithin-based (AndroMed®) and two egg yolk-based (BullXcell® and Optidyl®) commercially available extenders on post-thaw in vitro sperm quality. Fifty ejaculates collected from ten bulls were aliquoted into three parts and diluted with the above-mentioned extenders. Post-thaw sperm viability, mitochondrial membrane potential (MMP), plasma membrane integrity, and acrosome status were analysed immediately after thawing (0 h) and at an hourly interval during 2-h incubation at 38 °C. Sperm functionality variables were assessed by simultaneous quadruple staining using flow cytometry. Semen stored in Optidyl® had a greater viability, plasma membrane and acrosome integrity than that stored in AndroMed® and BullXcell® (P < 0.05). With the use of BullXcell® there was a higher percentage of sperm with high MMP (P < 0.05) when compared with the other extenders. The incubation affected the development of sperm quality parameters differently as the variables related to the plasma membrane showed an increase, while MMP and acrosome integrity showed a decline. Although the semen from all bulls responded to treatments in a similar manner, significant intra- and inter-male differences were found. In conclusion, the results clearly displayed the beneficial effects of egg yolk over soybean lecithin supplementation on in vitro sperm quality.