Effects of Sodium Butyrate on Sperm Function and Protein Acetylation in Fresh and Frozen–Thawed Boar Spermatozoa

Sodium butyrate (NaBu), a short-chain fatty acid and histone deacetylase inhibitor, has been reported to influence protein acetylation and cellular function; however, its effects on boar spermatozoa remain poorly understood. This study evaluated the effects of NaBu on sperm function and global protein acetylation in fresh after 24 h storage and frozen–thawed boar spermatozoa. Semen samples collected from boars (n = 4), with three ejaculates per boar, were supplemented with 0, 0.5, 0.75, or 1 mM NaBu, stored for 24 h at 17 °C, and subsequently cryopreserved. Sperm motility, mitochondrial membrane potential, membrane integrity, apoptosis-like changes, and chromatin status were assessed using CASA, flow cytometry, and fluorescence microscopy, whereas global protein acetylation was assessed by Western blotting. In fresh semen after 24 h storage, NaBu did not significantly affect the evaluated sperm functional parameters, whereas frozen–thawed spermatozoa showed significant changes in selected functional parameters, particularly total and progressive motility at 0.5 mM. Selected mitochondrial membrane potential parameters were also affected in frozen–thawed samples, while membrane integrity, apoptosis-like changes, and chromatin status remained largely unaffected. NaBu did not significantly alter global protein acetylation levels in either fresh after 24 h storage or frozen–thawed spermatozoa. Considerable inter-individual variability between boars was observed. These findings indicate that NaBu may affect selected in vitro functional properties of frozen–thawed boar spermatozoa; however, the observed functional changes were not associated with detectable statistically significant changes in global protein acetylation under the conditions tested. Further studies are needed to determine whether specific acetylated proteins, metabolic pathways, or stress-response mechanisms are involved.