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Impact of Exposure of Dairy Cow Feed to Polystyrene Microplastics on 24 h In Vitro Rumen Fermentation Responses, Microbiota Biodegradation Potential and Metabolic Pathways
Summary
Scientists found that when dairy cows eat feed contaminated with tiny plastic particles, it disrupts their digestion and changes the helpful bacteria in their stomachs. The cows' stomach bacteria can actually break down some of the plastic, but this process creates harmful chemicals that could affect milk production. This matters because microplastics are increasingly common in animal feed, which could potentially impact the safety and quality of dairy products we consume.
Microplastic pollution is increasingly serious worldwide, threatening human and animal health. The cow rumen is a key organ for nutrient digestion and absorption, and its fermentation is closely related to rumen microorganisms. Here, we investigated how polystyrene microplastics (PS-MPs) with varying particle sizes and concentrations affect rumen fermentation and the biodegradability of PS-MPs by rumen fermentation. The results reveal that exposure to PS-MPs lowered gas production and gas concentrations, as well as volatile fatty acid content, and these decreases were positively correlated with PS-MP concentration. However, higher PS-MP concentration and larger particle size increased the activity of carboxymethyl cellulose, β-glucosidase, and xylanase. Furthermore, PS-MP exposure reduced the abundance of certain rumen microorganisms and altered metabolic pathways and metabolites linked to PS-MP biodegradation. It was also found that PS-MP content decreased significantly after 24 h fermentation. Therefore, PS-MPs can inhibit rumen fermentation by affecting the rumen microbiome, and rumen microorganisms and their secreted enzymes can biodegrade PS-MPs to produce styrene and derivatives; such small molecules may further disrupt rumen homeostasis, thereby affecting lactation performance. In addition, rumen microbial degradation of PS-MPs provides a new idea to resolve future microplastic contamination challenges.