A massive collaborative study undertaken by Chinese and US researchers – who sampled 4 017 manure specimens from pigs, chickens and cattle in 26 countries over 14 years – found that worldwide, livestock manure is packed with antibiotic resistant genes (ARGs) that could threaten human health.
Their findings, published in Science Advances, show they found a substantial reservoir of known (2 291 subtypes) and latent ARGs (3 166 subtypes). The detections conferred potential resistance to 30 antibiotic classes, reports CIDRAP.
Chicken manure showed the highest ARG diversity, followed by swine and cow manure. On average, chicken and swine samples contained 2.0 times the ARGs of that found in human faeces, 2.5 times of that in sewage, and 18.3 times of that in soil.
“This research shows that what happens on farms doesn’t stay on farms,” said James Tiedje, PhD, one of the authors of the study, from Michigan State University.
“Genes from manure can make their way into the water we drink, the food we eat and the bacteria that make us sick.”
Chinese pig samples highest levels
The authors then took additional information about clinical significance, potential for mobility, and higher risk ARGs to make a predictive global map of livestock resistome risks that can help guide research and policy.
They found that swine manure diversity in Asia (246 ARGs) and abundance (3.93 copies per cell) was significantly higher than on other continents, specifically for aminoglycoside and tetracycline resistance gene abundance. The chicken manure diversity was highest in the European samples, despite Scandinavian countries having some of the lowest rates of detection.
North America had the highest detections among bovine manure samples, with Canada having the most ARGs detected, followed by the United States.
“As the world's largest pig producer, accounting for more than 50% of the global pig population, China displays higher bacterial abundance, diversity, and RSs (risk score) in pig manure than all other countries,” the authors wrote.
“As the leading beef producers, the United States and Brazil exhibit notably higher resistome abundance and diversity in cattle manure compared with other countries, with the exception of Canada.”
Helpful One Health tool
The authors said their map could be used as a helpful One Health tool as countries battle antimicrobial resistance. According to the World Health Organisation, antimicrobial resistance killed at least 1.27m people worldwide, and was associated with nearly 5m deaths, in 2019.
“There’s been a global push to reduce antibiotics in agriculture,” said Tiedje. “Denmark and other European countries led the way by banning growth-promotion antibiotics years ago and they’ve seen lower resistance levels as a result.”
Study details
Global health risks lurking in livestock resistome
Bintao Li, Lan Jiang, Timothy Johnson et al.
Published in Science Advances on 27 June 2025
Abstract
Livestock farming consumes more than 70% of global antibiotics annually, making livestock manures an important vector of anthropogenically influenced antibiotic resistance genes (ARGs). The global pattern of the livestock resistome, its driving mechanisms, and transmission potential to the clinic are not well assessed. We analysed 4017 livestock manure metagenomes from 26 countries and constructed a comprehensive catalog of livestock ARGs and metagenome-assembled genomes. Livestock resistome is a substantial reservoir of known (2291 subtypes) and latent ARGs (3166 subtypes) and is highly connectable to human resistomes. We depicted the global pattern of livestock resistome and prevalence of clinically critical ARGs, highlighting the role of farm and human antibiotic stewardship in shaping livestock resistome. We developed a risk-assessment framework by integrating mobility potential, clinical significance, and host pathogenic relevance, and prioritised higher risk livestock ARGs, producing a predictive global map of livestock resistome risks that can help guide research and policy.
Science Advances article – Global health risks lurking in livestock resistome (Open access)
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