Antibiotics in cattle leave their mark in dung

Overuse of antibiotics in livestock can spread drug-resistant microbes — via farm workers or even breezy weather. But there’s more than one reason stay upwind of drugged cattle.

Dung beetles (Aphodius fossor) make their living on cattle dung pats, which are rich in nutritious microbes. To investigate the effects of cattle antibiotics on this smaller scale, Tobin Hammer of the University of Colorado at Boulder and his colleagues studied the tiny communities around tetracycline-dosed and undosed cows. Compared with untreated cows’ dung, microbes in dung produced by treated cows were less diverse and dominated by a genus with documented resistance, the researchers report May 25 in the Proceedings of the Royal Society B.

Beetles typically reduce methane gas wafting off dung, but pats from treated cows showed a 1.8-fold increase in methane output. How this might figure into greater cattle methane production remains to be studied, but Hammer and company speculate that the antibiotics may wipe out the bacterial competition for microbial methane factories.