Impact of polyethylene terephthalate microplastics on feed digestive efficiency in ruminants

The increasing accumulation of microplastics (MPs) in agricultural systems poses a significant threat to the digestive efficiency in ruminants. This study investigated the effects of adding polyethylene terephthalate (PET) MPs at concentrations of 5 and 10 g/L in buffer-ruminal gastrointestinal solutions on ruminal degradability, gastrointestinal digestibility of rumen-undegraded residue, and total tract digestibility of corn silage and mixed hay using an in vitro model. Results showed that at the highest PET MP concentration (10 g/L), crude protein degradability decreased by 9% for corn silage and 8% for mixed hay. A reduction in neutral detergent fiber degradability was observed exclusively in mixed hay at the highest PET MP concentrations, with a decrease of 5%. Dry matter and acid detergent fiber degradability remained unaffected. In the gastrointestinal phase, crude protein digestibility of rumen-undegraded residue was reduced by 9% in mixed hay at the lowest PET MP concentration (5 g/L), while dry matter digestibility of rumen-undegraded residue remained unchanged. The total digestibility of crude protein in mixed hay decreased by 5% at both PET MP levels, while for corn silage, it decreased by 3% only at the highest PET MP concentration. Total dry matter digestibility remained unaffected. These findings demonstrate that PET MPs are not inert within the ruminant digestive system and can impair digestive efficiency, with more significant effects observed in mixed hay.