Microplastics‑cadmium co-exposure disrupts cow rumen fermentation via microbial and metabolic reprogramming

PLA adsorbs and releases more Cd than PVC, amplifying rumen disruption. • MPs–Cd inhibited hydrolase activity and disrupted carbon‑nitrogen metabolism. • MPs–Cd reduced fermentative taxa but promoted the growth of potential pathogens. • PLA–Cd disturbed nitrogen metabolism, while PVC–Cd impaired lipid/energy pathways. • MPs act as Cd carriers, exacerbating rumen metabolic dysfunction. Microplastics (MPs) and cadmium (Cd) both occur frequently in livestock feed and husbandry environments, and can exert adverse impacts on animal physiological homeostasis and core functional processes, particularly digestive physiology. However, the mechanisms underlying their combined effects and the roles of different MP types are not yet fully understood. Here, we employed a continuous multi-cycle in vitro rumen fermentation model to investigate the impacts of co -exposure to aged polylactic acid (PLA) and polyvinyl chloride (PVC) MPs with Cd on rumen fermentation characteristics, microbial community structure, and metabolic profiles. The results demonstrated that PLA exhibited stronger Cd adsorption and greater Cd-release efficiency compared with PVC. Co-exposure markedly inhibited hydrolytic enzymes, reduced total volatile fatty acid and gas production, and decreased fermentative taxa such as Bacteroidetes and Bacillota , while favoring potential pathogens. Non-targeted metabolomics further revealed that PLA–Cd exerted a stronger influence on nitrogen metabolism, whereas PVC–Cd caused more pronounced disturbances in lipid and energy metabolism. Microbiome–metabolite network analysis revealed a more fragmented structure under PLA–Cd treatment, indicating greater perturbation of microbial–metabolic interactions. Overall, MPs act as Cd carriers, substantially threatening ruminant health by reshaping microbial composition and fermentation metabolism. This study underscores the risks of combined MP and heavy-metal pollution and calls for re-evaluating the environmental safety of biodegradable plastics in agriculture. Download: Download high-res image (171KB) Download: Download full-size image