PSXI-23 Prevalence of Antibiotic Resistance Genes and Bacterial Community Diversity from Feces of Pasture-Raised Broiler and Layer Chickens, Swine, and Beef Cattle in the Southeastern USA

Abstract Animal manure can be a source of antibiotic resistant genes (ARGs) and pharmaceutical residues; however, few studies have been conducted to evaluate the presence of ARGs in pastured livestock systems. The objective was to determine the effects of four pasture-raised livestock species (broiler and layer chickens, swine, and beef cattle) on three different farms on fecal antibiotic residues (AR), microbial community diversity (MCD), and ARGs. Fecal DNA was collected (25 g each), homogenized, and extracted (0.2 g) using a Fecal/Soil Microbe DNA MimiPrep Kit. 16S rRNA, an estimate of the total MCD, was sequenced. Sulfonamide (Sul; Sul1) and tetracycline (Tet; TetA) ARGs were enumerated by qPCR. The results indicated that average fecal Tet AR tended to be greater (P = 0.09) for broiler chickens (11.4 µg kg-1) than for other livestock species (1.8-0.06 µg kg1), while chlortetracycline, lincomycine, oxytetracycline, and sulfachloropyridazine AR were similar among livestock species. There were interactions (P < 0.01) between farms and animal species for fecal pH and concentrations of total carbon, magnesium, sulfur, copper, and lead across animal species. In addition, cattle and swine samples showed a high degree of variability (α- and □-diversities) in fecal MCD, compared to broiler and layer fecal samples (P < 0.01). Firmicutes were the most abundant bacterial phylum in broiler (85.3%) and layer (80.0%) chickens (P < 0.01), as compared to swine (64.4%) and cattle (62.1%). The Sul1 (P < 0.05) and TetA (P < 0.001) ARGs in layer hens were the highest (16.5 x 10–4 and 1.4 x 10–4), followed by broiler chickens (2.9 x 10–4 and 1.7 x 10–4), swine (0.22 x 10–4 and 0.20 x 10–4), and beef cattle (0.19 x 10–4 and 0.02 x 10–4). This study indicated that individual farm management practices and specific animal species affected content of fecal AR, the fecal MCD, and ARG status in pasture-raised animals.