Microplastics contamination in dairy cows' total mixed ration

The demand for milk and meat is continuously increasing with the growth of world population, that is expected to reach about 9.7 billion by 2050. Ruminants are one of the main sources of these animal products, thus boosting their intensive livestock. However, ruminants are exposed to a huge number of contaminants, with potential risks for humans. Among contaminants, plastic materials are probably the most common. Low-density polyethylene (LDPE) and polyamide copolymer (PA-LDPE) films are widely used to cover horizontal silos and to wrap and tie bales; veterinary medicine containers are made of high-density polyethylene (HDPE). In addition, plastics from atmospheric deposition should be accounted in feed contamination studies. Plastics undergo to a systematic fragmentation driven mainly by ultraviolet radiation (UV) and mechanical abrasion, thus generating small plastic fragments (< 5 mm), called microplastics (MPs). Recent studies have shown that MPs can potentially contaminate animal feeds, as confirmed by their presence in cow blood and sheep feces. Aim of this work was to verify the presence of MPs in a total mixed ration (TMR) for dairy cows using a protocol specifically optimized to extract 5 polymers: LDPE, HDPE, PA, polyethylene terephthalate (PET) and polystyrene (PS). The TMR was sampled in 3 different points of the feed lane of a dairy cattle farm located near Torino (N-W Italy). No plastic disposables or materials were used for sampling or analysis. Samples were dried at 60°C overnight and grounded with a mill (5 mm sieve). The MPs extraction was done with an environmental control blank using a basic digestion followed by Fenton reactions. MPs were finally recovered and quantified using a stereomicroscope. An average of 17 MPs/g was found in the TMR. Most MPs were fibers of different colors (colorless, black, red and blue). The length ranged from 0.201 mm to 3.734 mm. In this trial we extracted for the first time MPs from dairy cows’ TMR and we verified the MPs presence in the animals diet. The incidence of MPs contaminations of TMRs and feeds (corn silage, hay and concentrate) is under investigation in different farms, as part of a larger project for the optimization of MPs extraction protocol of feeds and animal diets.