Among researchers' findings:
• The mass of particulate matter (PM) collected downwind of feedyards was significantly different than that collected immediately upwind of each feedyard.
• Monensin, an antibiotic, was detected in 100 percent of particulate matter samples downwind and upwind of feedyards while tylosin, a macrolide antibiotic, was detected in 80 percent of samples downwind of feedyards; and
• Three tetracycline antibiotics (tetracycline, chlortetracycline, and oxytetracycline) were detected together in 60 percent of particulate matter samples downwind of feedyards.
The study also showed six targeted tetracycline resistance genes were significantly more abundant in particulate matter collected downwind of feedyards compared to upwind. But researchers also found no significant correlation between tetracycline concentrations in particulate matter and tetracycline resistance gene abundance.
“Given the extent of confined beef cattle production, extensive use of veterinary antibiotics, and significant wind energy potentials in the Central Plains Region of the United States, we hypothesized that antibiotics and antibiotic resistant bacteria in PM collected downwind of beef cattle feedyards would be abundant compared to that in corresponding upwind PM,” the researchers said. “To address our hypothesis, we quantified antibiotics commonly administered in animal-based agriculture, assessed microbial community composition, and assessed occurrence of antibiotic resistance genes in airborne PM emanating from beef cattle feeding operations.”
Researchers collected particulate matter downwind and upwind of 10 beef cattle feedyards. From the particulate matter, researchers quantified six veterinary antibiotics in addition to antibiotic resistance genes.
The study noted that an estimated 10 million kg of antibiotics per year are used in animal agriculture. Antibiotics used for growth promotion are added to livestock feed and are incompletely metabolized and poorly absorbed in the animals’ gastrointestinal tracts. Upon excretion, researchers said, the wind may carry compounds in particulate matter. Also, antibiotics and other compounds may spread beyond feedyards through application of manure onto agricultural fields and rainwater runoff.
“Once in the environment, antibiotics can facilitate de novo development of bacterial antibiotic resistance and provide a selective advantage for bacteria that acquire resistance either in treated animals or in the environment,” the researchers wrote.