Antibiotic Residues in Muscle Tissues of Lueyang Black-Bone Chickens Under Free-Range Mountainous Conditions and Their Association with Gut Microbiota.

The absorption, transport, and distribution of antibiotics in animals are influenced by the composition and function of the intestinal microbial community. However, most existing studies have focused on intensive farming systems involving the artificial addition of antibiotics. For free-range local chicken breeds in mountainous areas without antibiotic additives, systematic research on the presence of antibiotic residues in their muscle tissues and their association with the gut microbiota is lacking. Therefore, in this study, mountainous free-range Lueyang black-bone chickens were selected as the research subjects, employing non-targeted metabolomics and microbiomics to analyze the distribution of antibiotics in intestinal tissues (duodenum and caecum) and muscle tissues (breast and leg muscles), and their correlations with the intestinal microbiota. Metabolomics detected 47 antibiotics in intestinal tissues and 22 in muscle tissues, with 9 common to both tissues, including clinically and veterinary relevant antibiotics such as oxacillin, kanamycin, and tobramycin. Microbiomics analysis indicated significant differences in microbial communities between the duodenum and caecum at the genus level. LEfSe analysis identified seven characteristic genera in the duodenum (e.g., Bacteroides, Alistipes) and five in the caecum (e.g., Lactobacillus, Ureaplasma). Pearson correlation analysis further revealed that these shared antibiotics were significantly associated with the differential genera in the intestine. For instance, oxacillin exhibited a positive correlation with both Bacteroides and Alistipes. Kanamycin was positively correlated with Alistipes, whereas tobramycin showed a negative correlation with Bacteroides. These results indicate that antibiotic residues were present in both intestinal and muscle tissues of Lueyang black-bone chickens raised under free-range mountainous conditions. The nine antibiotics common to both tissues are likely absorbed in the intestines and transported to muscles via the bloodstream. It is hypothesized that the gut microbiota may play a potential regulatory role in this process, providing a theoretical basis for understanding microecological mechanisms under environmental antibiotic exposure.