Drugs and dung a bad mix for climate: antibiotics boost cattle methane emissions, study finds

Scientists have discovered a potential threat to Earth’s climate lurking in a dark and smelly place: the dung of cattle treated with antibiotics, a study said Wednesday.

Lab studies revealed that dung from animals given a common antibiotic gave off more than double the methane, a potent greenhouse gas, than those of non-treated cows, a team wrote in the journal Proceedings of the Royal Society B.

This highlights another danger of routinely using antibiotics on livestock, a practice which has already created a wave of drug resistance in humans.

“Antibiotics are extensively used in agriculture to promote growth and to treat or prevent livestock disease, yet they may have major consequences for human and environmental health,” wrote the study authors.

“We provide the first demonstration that antibiotics can increase dung emissions of methane.”

The team collected dung from 10 cows - five given a three-day course of a common broad-spectrum antibiotic called tetracycline, and five given none.

In decidedly unglamorous work, they divided the dung into smaller pats, which they placed in open buckets in the field along with a few empty ones, to measure and compare flows of gases like carbon dioxide, methane and nitrous oxide.