Deciphering the microbiome, lipopolysaccharides, and metabolome interplay: Unveiling putrescine's mechanism for enhancing sperm quality in heat-stressed boars.

Global warming has added to concerns regarding declining male fertility due to high temperatures. As a metabolite of arginine, putrescine improves gut health and promotes testicular development in boar; however, its action in improving semen quality under heat stress is unknown. Therefore, we assessed the effect of putrescine on the semen quality of boars in a heat stress model. Results showed that putrescine ameliorated the heat stress-induced decline in semen quality and testosterone levels in boars, confirmed by sperm viability, immobility rate, and apoptosis levels. Fecal microbial 16S rRNA sequencing showed that heat stress induces intestinal microecological dysregulation triggering an increase in the serum lipopolysaccharide (LPS) levels and reducing boar semen quality. A negative correlation between the Lachnospiraceae_XPB1014_group and LPS-binding protein (LBP) levels was observed. The Lachnospiraceae_XPB1014_group was reduced significantly under heat stress, and its relative abundance significantly increased after putrescine diet, which reduced both LPS and LBP in the serum of heat-stressed boars. Heat stress also affected plasma amino acid metabolism, and the regulation of plasma metabolism by putrescine can be attributed to its effects on LPS and the LBP owing to the significantly correlation of both with multiple plasma differential metabolites. Putrescine is thus considered to inhibit the increased serum LPS by acting on intestinal microorganisms, particularly by increasing the relative abundance of the Lachnospiraceae_XPB1014_group, and further modulate plasma amino acid metabolism to improve the semen quality in heat-stressed boars.