Quality of boar spermatozoa from the sperm-peak portion of the ejaculate after simplified freezing in MiniFlatpacks compared to the remaining spermatozoa of the sperm-rich fraction

Abstract

Boar sperm viability post-thaw differs depending on the ejaculate fraction used, with spermatozoa present in the first 10 mL of the sperm-rich fraction (SRF) (portion 1, P1, sperm-peak portion) displaying the best cryosurvival in vitro compared with that of spermatozoa from the rest of the ejaculate (portion 2 of the SRF plus the post-spermatic fraction), even when using simplified freezing routines. This viability apparently relates to the specific profile of seminal plasma in P1 (i.e., glycoprotein and bicarbonate concentrations, and pH). However, spermatozoa from P1 have not been compared with spermatozoa from the rest of the SRF (SRF–P1, usually 30–40 mL of the SRF), which is routinely used for freezing. We compared P1 with SRF–P1 in terms of sperm kinematics (using the QualiSperm™ system), while membrane integrity (SYBR-14/PI), acrosome integrity (FITC PNA/PI), and sperm membrane stability (Annexin-V) were explored using flow cytometry. As well, total protein concentration and the proteomics of the seminal plasma (SP) of both portions of the SRF were studied using two-dimensional electrophoresis (2DE), mass fingerprinting (MALDI-TOF), and collision-induced dissociation tandem mass spectrometry (CID-MS/MS) on selected peptides. The SRF portions were collected weekly from four mature boars (4–5 replicates per boar, sperm concentration: P1, 1.86 ± 0.20; SRF–P1, 1.25 ± 0.14 × 109 spz/mL) and processed using a quick freezing method in MiniFlatPacks. Post-thaw sperm motility reached 50%, without differences between SRF portions, but with clear inter-boar variation. Neither plasma membrane nor acrosome integrity differed (ns) between fractions. These results indicate that there are no differences in cryosurvival after quick freezing of boar spermatozoa derived from either of the two SRF portions. While P1 and SRF–P1 clearly differed in relative total protein contents, as expected, they displayed very similar protein profiles as assessed using 2DE and mass spectrometry (tryptic peptide mass fingerprint analysis and CID-MS/MS), indicating a similar emission of epididymal protein content.