Long-term grazing does not increase antibiotic resistance genes in the soil in an Inner Mongolia desert steppe.

Antibiotic resistance due to overuse of antibiotics is one of the biggest challenges to global health. Furthermore, antibiotic resistance genes (ARGs) can enter the environment, for example, via the accumulation of animal excreta. However, the effect of different levels of livestock grazing under natural grazing conditions on soil ARGs is not yet clear. In this study, we examined soil ARGs from a long-term experiment manipulating levels of grazing intensity in an Inner Mongolian desert steppe using metagenomic sequencing technology. We found little influence of increasing grazing intensity on the abundances of soil ARGs. We did, however, find decreases in the absolute abundance of aminoglycoside ARGs with light grazing and increases of vancomycin ARGs under heavy grazing. We found that grazing indirectly affects soil ARGs by altering soil physicochemical properties (moisture, C/N) and bacterial diversity. Our study suggests that long-term grazing will not significantly increase ARGs in the soil of the desert steppe of Inner Mongolia. At the same time, we also believe that the risk of spreading ARGs is lower under light grazing.