Microbiota and metabolic perturbations in bull semen: Links to heat stress-induced quality decline

Heat stress (HS) poses a major environmental issue that negatively impacts the reproductive efficiency of bulls. However, the complex interactions among HS-induced declines in semen quality, sperm metabolism, and semen microbiota remain inadequately understood. The study explored the effects of HS on the quality of bull semen, sperm metabolic profiles, and semen microbiota composition by employing 16S sequencing and metabolomics. The findings revealed that HS significantly compromised semen quality and altered the semen microbiota composition, as evidenced by increased abundances of Acholeplasma and Oceanivirga , and decreased abundances of Lactobacillus , Ruminococcaceae UCG-005 , and Ruminococcaceae UCG-010 . Metabolomic analysis indicated that HS predominantly affected the metabolic pathways of amino acids and carbohydrates in sperm. Spearman's correlation analysis suggested that HS-induced sperm metabolic disorders may be associated with dysbiosis in the semen microbiota composition in bulls. The study reveals new perspectives on the microbiota-metabolism relationship in semen quality impacted by HS, indicating potential approaches to counteract HS-related fertility reductions in bulls through microbiota interventions. • Heat stress altered the semen microbiota composition in bulls. • Heat stress altered sperm metabolism in bulls. • Heat stress induced sperm metabolic disorders associated with semen microbiota composition dysbiosis