Abstract Background Enhancing sperm motility is crucial for improving male fertility in ruminants. The rumen microbiota, central to nutrient metabolism of ruminants, represents a promising yet underexplored target for dietary intervention. This study investigated whether N-acetylcysteine (NAC) improves sperm motility via modulating the rumen microbiota–metabolite axis. Results Dietary NAC supplementation significantly enhanced sperm motility in goats ( P < 0.05), with the optimal effect observed at 0.3%, which coincided with improvements in sperm membrane integrity, antioxidant capacity, and mitochondrial function. Functional analysis revealed that NAC-induced microbial remodeling enriched KEGG pathways involved in antioxidant, energy, and lipid metabolism. Correspondingly, beneficial bacteria such as Pediococcus pentosaceus , Bacteroides acidifaciens , and Akkermansia , among others, were significantly enriched ( P < 0.05). Notably, metabolic alterations in these pathways were consistently reflected in both the rumen fluid and plasma metabolomes, as evidenced by 25 conserved pathways and 2 overlapping metabolites. Collectively, these metabolic alterations ultimately enhanced sperm motility by improving sperm antioxidant status, energy supply, and lipid homeostasis. Conclusions Our study thus reveals that NAC enhances sperm motility via a rumen microbiome-mediated “rumen–plasma–sperm” axis. This novel insight broadens the understanding of how NAC—and potentially other antioxidants—regulates sperm motility, highlighting the promise of NAC-based dietary interventions for improving reproductive performance. Graphical Abstract
Luo et al. (Sun,) studied this question.