Animal feces are often used for the nutritional enrichment of agricultural soils; however, fecal matter also can be a major reservoir of antibiotic-resistant bacteria and antibiotic resistance genes. Within the framework of the One Health approach, which recognizes the interconnectedness of human, animal, and environmental health, there is a growing concern for antibiotic resistance in farm waste and its significance as a source of the wider resistance spread. The domestic animals are often reared and treated under very different farming management systems, but the fecal resistance and the potential for resistance gene and bacteria transmission to the environment as a function of farming intensity has been largely overlooked. This is a huge omission because of the expected global increases in the use of antibiotics by 2030. Two-thirds of this increase is projected due to increasing numbers of domestic animals, but the remaining one-third is suggested because of shifts in farming toward more intensive systems (PNAS, 2015). Urgent preventative planning is needed to reducing the potential impact of farming intensification on global antibiotic resistance.

In this study, we used both genotype and phenotype approaches for our fecal samples taken from eight Chinese farms, where yak, sheep, pig, and horse were reared under free-range to intensive conditions, and fecal antibiotic resistance levels were quantified. Overall, intensification significantly increased antibiotic resistance genotypes and phenotypes in associated feces from various animals, no matter yak, sheep, pig, or horse were investigated. Behind this is the high occurrence of mobile genetic elements that can accelerate transmission and the frequent co-location of such genes with antibiotic resistance genes, raising concerns for potential resistance development in pathogens, including multidrug resistance strains.

Farming intensification is a global trend for satisfying the world’s food needs. As said in UN special report, "failing to address the global burden of antimicrobial resistance, including its environmental dimensions, could take humanity back to an era when even mild infections could become deadly”. Our results here show that antibiotic resistance in feces shed by animals will increase as farming intensification occurs, which has massive implications to the development, transmission and spread of resistance related to animal operations. Prevention must start now.

As a first step, we can strongly retain the traditional free-range ways for animal farming whenever possible or, if not possible, promote the development of improved on-farm strategies, such as reducing the dependence on antibiotics for non-therapeutic purposes, and improving barriers between animals and farm activity from the wider environment, such as improved treatment and disposal of animal wastes, particularly from intensive farms. We are at a crossroad for reducing global antibiotic resistance. Prevention is critical now if we want to produce enough food for the world and reduce the potential for superbugs in global health care systems. (Text/written by Hang Wang and edited by David Graham and Yong-Guan Zhu).