Objectives: The Taihe Black-Boned Silky Fowl (TBSF) is a unique indigenous chicken breed in China, characterized by widespread melanin deposition throughout its body. Fluoroquinolones (FQs) such as enrofloxacin can persist in TBSF for an extended period exceeding 100 days. The aim of this study was to examine the current status and development trends of FQ resistance within the TBSF breeding environment. Methods: Whole-genome sequencing was utilized to identify the molecular presence of quinolone resistance-determining region (QRDR) mutations and plasmid-mediated quinolone resistance (PMQR) genes in Escherichia coli isolates obtained from TBSF farms. Network inference based on strong Spearman correlations (ρ > 0.5) and statistically significant associations (p-value < 0.05) was applied to investigate the co-occurrence patterns among FQ residues, resistance phenotypes, and antibiotic resistance genes. Results: The results showed that FQ residues were identified as the primary contributor to FQ resistance in E. coli isolates. Mutations at QRDR sites were the predominant factor driving FQ resistance, rather than PMQR determinants. This study also reported the first identification of GyrA-S83Q mutation being associated with FQ resistance. Conclusions: It was concluded that E. coli strains in TBSF environments, where chickens have a long-term residual metabolic cycle of antimicrobials, may develop and evolve new mechanisms to adapt to this environment. Further research is warranted to investigate the evolution of FQ resistance in E. coli strains within TBSF environments.

Black-bone fowls are rich in melanin and regarded as being rich in nutritional value. However, the metabolism of antibiotics in black-bone fowls remains poorly understood. This study aimed to determine the tissue residue depletion kinetics of Sulfamonomethoxine (SMM) or Doxycycline in Taihe black-bone silky fowls. The tissue residue experiments involved a total of two hundred and forty Taihe black-boned silky fowls. The birds were raised to 100 days old in the same laboratory conditions and divided into a control group, SMM group, and Doxycycline group (80 birds for each group). The control group was provided normal drinking water. The SMM group was oral-administered SMM at concentrations of 50 mg/kg bw per day, and the Doxycycline group was oral-administered Doxycycline at concentrations of 40 mg/kg bw for 5 days, respectively. After the last dose, liver, kidney, muscle, and skin/fat were collected at various time points (0.16, 1, 3, 5, 7, 9, 12, 20, 30, and 40 days, eight birds for each time point). Concentrations of SMM or Doxycycline were analyzed using the UPLC–MS/MS method. The terminal elimination half-lives of SMM in muscle, skin/fat, liver, and kidney were 1.82 ± 1.24, 15.3 ± 4.97, 4.36 ± 1.49, and 5.42 ± 3.46 days, respectively, and 8.62 ± 2.82, 6.88 ± 2.06, 4.12 ± 1.28, and 1.53 ± 0.28 days for Doxycycline. The estimated withdrawal times (WDIs) of SMM were 4, 27, 10, and 12 days, while the estimated WDIs of Doxycycline were 18, 15, 4, and 6 days for muscle, skin/fat, liver, and kidney, respectively. The SMM or Doxycycline bioaccumulate in the skin/fat and may cause antimicrobial residues to be absorbed by human when the skin/fat is used in the diet. Doxycycline persists in muscle for a longer duration compared to SMM. This highlights the significance of muscle and skin/fat as a target organ for future food safety research.

Objective To explore the withdrawal time of veterinary drugs in laying hens before laying，the accumulation and elimination of florfenicol in eggs of laying hens were examined after oral administration to laying hens before laying，and results can provide scientific support for laying hens breeding industry. Method 378 healthy Lehmann Pink hens were orally administrated with florfenicol at a therapeutic dose，and the florfenicol and florfenicol amine residues in egg samples were determined by liquid chromatography-tandem mass spectrometry.The withdrawal time of florfenicol in laying hens before laying was determined by using the residue elimination model and software WT1.4. Result Results showed that the total residues of florfenicol and florfenicol amine in eggs were gradually increased during administration and reached the peak value（about 307.64 μg/kg）1 d after the drug was stopped，and then the drug residues were gradually decreased with the extension of drug withdrawal time.After 10-day withdrawal time，the total residues of florfenicol and its metabolites in eggs decreased to below the maximum residue limit（MRL）of 10 μg/kg and eventually belowed the detection limit on day 12 post-treatment.Based on the drug residue elimination model and software WT1.4，the withdrawal times of 9.70 d and 10.26 d for florfenicol were acquired.Verification results showed that the total concentrations of florfenicol and florfenicol amine residues in all egg samples belowed 10 μg/kg after 9-day withdrawal time.Based on above results，a 10-day safety interval was recommended for florfenoicol in laying hens before laying.The time interval from the first egg production to the theoretical laying time was 32 d during the experiment period. Conclusion Due to the irregularity of eggs production during early laying period，a 42-day withdrawal time is recommended for the florfenicol powder in laying hens before laying，to protect the health of egg consumers.

Selenium is a widely utilized supplement in poultry production. Its bioavailability and tissue deposition vary with chemical form and may affect the gut microenvironment. Taihe Black-Boned Silky Fowl (TBSF), a Chinese endemic breed with systemic melanin deposition, exhibit enhanced absorption and enrichment of diverse compounds. As a metalloid, selenium may also promote antimicrobial resistance in microbiomes, including those of the gut. However, its impact on the TBSF gut microbiota and resistome remains unknown. We therefore investigated how selenium chemical form influences the cecal microbiome and resistome. Four dietary treatment groups of TBSF (n = 120 birds per group; 60 males and 60 females) were fed for 80 days: CK (selenium-deficient control), YS (sodium selenite), JS (yeast-derived selenium), and DS (selenomethionine), with measured dietary selenium concentrations of 0.05 ± 0.002, 0.33 ± 0.023, 0.35 ± 0.017, and 0.36 ± 0.042 mg/kg, respectively. We performed metagenomic sequencing analysis to assess alterations in microbial composition and resistome profiles in cecum. Results demonstrated that selenium supplementation significantly modulated cecal microbiota structure in both male and female birds(Bray-Curtis distance-based analysis, Wilcoxon rank-sum test, P < 0.05), with pronounced sex-dependent differences. The relative abundances of three prevalent antibiotic resistance genes (ARGs), bcrA, efrA, and fusA, were significantly elevated in selenium-supplemented groups compared with the CK group (Kruskal-Wallis H test, FDR-adjusted P < 0.05). Selenium supplementation reduced mobile genetic element (MGE) type diversity while increasing overall MGE relative abundance. Transposases and recombinases were the two most abundant MGE-associated functional classes. Mantel correlation analysis revealed strong associations between cecal microbiota composition and both ARG and MGE profiles (r ≥ 0.5, P ≤ 0.001). The sexually dimorphic cecal microbiota composition in TBSF may underlie the observed sex-dependent resistome response: sodium selenite exerted the strongest effect on ARG and MGE enrichment in roosters, whereas yeast-derived selenium induced the strongest effect in hens. Further network analysis revealed that sodium selenite exerted the most pronounced influence on resistome-microbiota co-occurrence patterns. These findings underscored the dual-sided nature of selenium supplementation from the perspective of ARGs, indicating that selenium supplementation may alter the composition of the cecal microbiota, thereby modulating the relative abundance and community structure of ARGs and MGEs in the TBSF cecum. Given selenium's essential role and narrow therapeutic index, its chemical form and dosage must be evidence-based and rigorously optimized to minimize potential unintended contributions to antimicrobial resistance. This represents a potential ecological and antimicrobial resistance concern from a One Health perspective that warrants further investigation.