Chromatin condensation but not DNA integrity of pig sperm is greater in the sperm-rich fraction

Abstract

Background protamination and condensation of sperm chromatin as well as DNA integrity play an essential role during fertilization and embryo development. In some mammals, like pigs, ejaculates are emitted in three separate fractions: pre-sperm, sperm-rich (SRF) and post sperm-rich (PSRF). These fractions are known to vary in volume, sperm concentration and quality, as well as in the origin and composition of seminal plasma (SP), with differences being also observed within the SRF one. Yet, whether disparities in the DNA integrity and chromatin condensation and protamination of their sperm exist has not been interrogated. Results This study determined chromatin protamination (Chromomycin A3 test, CMA3), condensation (Dibromobi‑mane test, DBB), and DNA integrity (Comet assay) in the pig sperm contained in the frst 10 mL of the SRF (SRF-P1), the remaining portion of the sperm-rich fraction (SRF-P2), and the post sperm-rich fraction (PSRF). While chromatin protamination was found to be similar between the diferent ejaculate fractions (P>0.05), chromatin condensation was seen to be greater in SRF-P1 and SRF-P2 than in the PSRF (P=0.018 and P=0.004, respectively). Regarding DNA integrity, no diferences between fractions were observed (P>0.05). As the SRF-P1 has the highest sperm concentra‑tion and ejaculate fractions are known to difer in antioxidant composition, the oxidative stress index (OSi) in SP, calcu‑ lated as total oxidant activity divided by total antioxidant capacity, was tested and confrmed to be higher in the SRFP1 than in SRF-P2 and PSRF (0.42±0.06 vs. 0.23±0.09 and 0.08±0.00, respectively; P<0.01); this index, in addition, was observed to be correlated to the sperm concentration of each fraction (Rs=0.973; P<0.001). Conclusion While sperm DNA integrity was not found to difer between ejaculate fractions, SRF-P1 and SRF-P2 were observed to exhibit greater chromatin condensation than the PSRF. This could be related to the OSi of each fraction.