Polystyrene microplastics compromise intestinal health and reduce growth and slaughter performance of Chahua chicken No. 2.

Microplastics are ubiquitous in livestock settings and raise increasing concern, yet studies on their effects on poultry intestinal health and gut microbiota, particularly in native Chinese breeds, are still scarce. Chahua chicken No. 2 were exposed to drinking water with 0, 0.05, 0.1, or 0.5 mg/d polystyrene microplastics (PS-MPs). At 0.5 mg/d, PS-MPs significantly reduced body weight, average daily gain, and feed intake at 42 and 120 days, while increasing feed conversion ratio and decreasing carcass traits (semi-eviscerated yield, eviscerated yield, breast and thigh muscle weights) at 42 days (p < 0.05). This dose also increased the microplastic-associated fluorescence signal in jejunum and ileum, reduced villus height and villus height/crypt depth ratio, and deepened crypts. It downregulated genes associated with intestinal barrier integrity (ZO-1, Occludin, Claudin-1), upregulated inflammatory cytokines (IL-6, IL-8, IL-1β, TNF-α, MIP-1β), and suppressed genes involved in glucose (SLC5A1 and SLC2A2), lipid (SLC27A4, APOA1, APOB, MTTP, CD36, FABP2), and amino acid (SLC15A1, SLC7A1, SLC7A9, SLC3A1, SLC6A19) transport (p < 0.05). 16S rRNA gene sequencing analysis revealed that 0.5 mg/d PS-MPs exposure induced intestinal microbiota dysbiosis in Chahua chicken No. 2, characterized by an increased abundance of norank_o_Clostridia_UCG_014, Mediterraneibacter, Olsenella, and Faecalitalea (p < 0.05). Overall, these findings indicate that PS-MP exposure is associated with alterations in growth performance, intestinal morphology, barrier-related gene expression, inflammatory responses, nutrient transporter expression, and gut microbiota in Chahua chicken No. 2.