Comparative Study of Different Methods for Plasma Membrane Integrity Assessment of Frozen-thawed Boar Spermatozoa

In this study, different assays were used to assess the structural and functional integrity of the sperm plasma membrane following freezing-thawing of the whole ejaculates (WEs) and sperm-rich fractions (SRFs) of boar semen. Besides sperm viability assessments (motility and mitochondrial membrane potential using a mitochondrial specific dye, JC-1 with propidium iodide, PI), sperm plasma membrane integrity (PMI) assessments were determined simultaneously using different membrane-based tests (SYBR14/PI and carboxyfluorescein diacetate (CFDA) with PI (CFDA/PI), and the hypo-osmotic swelling (HOS) test). ANOVA results showed that boar variability had a significant effect on the analysed parameters of post-thaw sperm characteristics. Spermatozoa harvested from the WEs exhibited a marked decline in post-thaw viability, manifested in reduced motility and mitochondrial membrane potential, than those originated from the SRFs after freezing-thawing. Cryopreservation compromised sperm PMI, as indicated in a significant decline in SYBR-stained, CFDA-stained or HOS-positive sperm cells, irrespective of the ejaculate collection procedure. It was observed that the membrane-based tests were strongly inter-correlated. Furthermore, agreement between the measurements of the membrane-based tests was confirmed by the Bland-Altman scatter plots of differences, suggesting that these tests could detect the same sperm cohorts, which were susceptible to cryo-induced membrane damage. The findings of this study indicate that dual fluorescent staining with SYBR-14/PI and CFDA/PI assays, in combination with the HOS test, provide more precise description of the sperm populations in frozen-thawed boar semen.