Family livestock waste: An ignored pollutant resource of antibiotic resistance genes.

The random discharge of livestock waste from family farms without utilization and treatment has caused great pressure on the rural ecological environment and gravely increased the environmental pollution. In this study, we targeted 26 family livestock farms to assess the occurrence characteristics of antibiotic resistance genes (ARGs) in livestock waste and its receiving farmland environment in Erhai Lake basin of China by real-time fluorescence quantitative PCR. The results showed that various common ARGs and some high-risk ARGs (i.e., bla, bla and bla) were prevalent in family livestock waste, and the pollution of tetracycline resistance genes was the most serious in these family livestock farms. Meanwhile, we also found that the ARG levels were higher in family chicken farms than that in pig and cattle farms, and ARGs pollution in layer waste and sow waste was more severe than that in broiler waste and piglet/fattening pig waste, respectively. Troublesomely, significant ARGs levels could be discharged via manure application, further causing the increase of ARGs abundance in soil environment (approximately 11-36 times). This study demonstrated the high prevalence and severity of ARGs contamination in family livestock farms, also emphasizing that family livestock waste was a non-ignored important pollutant resource of ARGs in the environment.