Polystyrene microplastics impair sheep spermatogenesis by disrupting rumen microbiota-derived butyrate signaling.

BACKGROUND: Microplastics are emerging environmental contaminants with male reproductive toxicity; however, their effects on ruminants and underlying mechanisms remain poorly understood. RESULTS: In this study, male Hu lambs were exposed to dietary polystyrene microplastics (PS-MPs) at 0, 75, and 150 mg/kg diet for 120 d, followed by a 180-d recovery period. PS-MPs exposure caused persistent testicular injury, characterized by disrupted seminiferous architecture and enhanced germ cell apoptosis. Single-cell transcriptomic analysis revealed impaired spermatogonial differentiation, accompanied by suppression of Nrf2-associated antioxidant responses. Metabolomic profiling further identified dysregulation of glutathione metabolism in both testis and plasma. Importantly, PS-MPs were not detected in testicular tissue, suggesting that detectable direct particle accumulation was unlikely to be the primary driver of toxicity. Instead, rumen analyses showed that PS-MPs altered microbial composition, notably reducing butyrate-producing bacteria, accompanied by sustained decreases in ruminal butyrate and circulating β-hydroxybutyrate (BHB). To investigate the potential involvement of rumen-derived butyrate in PS-MPs-induced testicular toxicity, sodium butyrate was supplemented to PS-MPs-exposed lambs. Dynamic analyses showed that ruminal butyrate recovered first, followed by circulating BHB, then systemic inflammation and oxidative status, and finally testicular damage was alleviated with restoration of Nrf2 signaling. CONCLUSIONS: These findings suggest that PS-MPs exposure disrupts spermatogenesis in sheep through rumen-derived butyrate alterations rather than detectable direct tissue accumulation. This study provides insight into microplastic-induced testicular toxicity and supports the rumen microbiota-metabolite axis as a potential mechanistic link underlying distal organ toxicity in ruminants.