Microplastics, tiny plastic particles pervasive in agricultural environments, interact with and disrupt the microbial ecosystem in the rumen – the first stomach chamber of cattle, reveals an international study.
“Our work is a first step toward understanding the biological consequences of microplastic exposure in farm animals,” said lead researcher Daniel Brugger, Associate Professor of Companion and Monogastric Production Animal Nutrition at the University of Helsinki. “There is an urgent need for in-vivo studies to better understand the impacts on animal health and food safety, especially as global plastic production continues to rise.”
The findings of a joint study from the University of Helsinki, University of Zurich, University of Hohenheim, and Technical University of Munich not only shed light on how microplastics are transformed within the digestive system of farm animals but also highlight potential risks for animal health, productivity, and food safety.
Using a controlled laboratory fermentation system, researchers incubated rumen fluid from cows with hay or barley and five common types of microplastics found in agricultural settings: polylactic acid (PLA), polyhydroxybutyrate (PHB), high-density polyethylene (HDPE), polyvinyl chloride (PVC), and polypropylene (PP). The microplastics were tested in various particle sizes and doses to evaluate their impact on rumen fermentation, microbial activity, and the plastics themselves.
The key findings of the study are:

• All tested microplastics did not remain inert in the rumen; instead, they interacted with the microbial ecosystem, altering fermentation and microbial functions.
• Their presence consistently reduced cumulative gas production, a key indicator of overall fermentation activity, regardless of plastic type, particle size, or dose.
• Total dry-matter disappearance increased with microplastic addition, suggesting that not only feed but also part of the plastic mass was broken down during fermentation, and potentially reduced microplastic size, increasing tissue penetration risk
• In barley-based incubations, microbial activity shifted, with proteins linked to stress responses increasing, while those involved in carbohydrate and amino-acid metabolism decreased - a pattern that is typical of a microbial stress response.

These results indicate that microplastics disturb normal microbial metabolism and are likely to be at least partially degraded into smaller fragments by rumen microbes.
Implications for agriculture and food safety

The study closes an important knowledge gap about how microplastics behave in the digestive systems of farm animals. While previous research has established that livestock are exposed to microplastics through contaminated soils and feed, it was unclear whether these particles remained unchanged or interacted with the microbiome.
“Our study shows for the first time that microplastics do not simply pass through the digestive tract of farm animals. Instead, they interact with the gut microbiome, alter fermentation processes, and are partially broken down,” says Jana Seifert, Professor of Functional Microbiology of Livestock at the University of Hohenheim, Germany. “This means farm animals are not passive recipients of plastic pollution; their digestive systems may act as bioreactors that transform microplastics and redistribute them within agricultural systems.”
However, the findings also raise significant concerns. A stressed, less efficient microbiome could negatively impact animal health and productivity. Additionally, smaller plastic fragments formed during digestion may be more easily absorbed into tissues, potentially entering the human food chain. This risk could be particularly pronounced in young or stressed animals with more permeable intestinal barriers.
How to avoid plastics ending up to the feed-food chain?

Researchers raise the need for better management of plastic use in agriculture, including silage films, packaging materials, and sewage sludge on fields, to reduce microplastic contamination in animal feed. “Plastic pollution isn’t just an environmental issue ‘out there.’ It has direct biological consequences for farm animals, and potentially for humans, through the food chain,” Cordt Zollfrank, Professor of Biogenic Polymers at the Technical University of Munich, Germany, emphasises.
The research also provides a scientific foundation for future risk assessments and monitoring. Regulators, veterinarians, and the feed industry now have experimental evidence that microplastics interact with the rumen microbiome and are partially transformed. This must be considered when defining acceptable contamination levels and developing methods to detect plastics in feed, manure, and animal products.
“Our findings may also help to inform future research on microplastic–microbiome interactions in non-ruminant species, such as pigs, although this still needs to be tested in those animals,” says Brugger.

About microplastics
While most people associate microplastics with oceans and marine life, a significant portion of plastic pollution ends up on farmland, eventually reaching animal feed and digestive systems. Microplastics have already been detected in livestock feed, manure, and even human stool samples, indicating their circulation through the feed–food chain.