Giving cattle antibiotics to encourage growth may be doing more than creating drug-resistant microbes. It may be boosting greenhouse gas emissions and contributing to climate change. As part of a recent study published in the Proceedings of the Royal Society B, researchers looked at the effect of a 3-day treatment of tetracycline on the amount of methane generated in the manure of cattle. Methane is a powerful greenhouse gas. The research showed that methane emissions from the manure of antibiotic treated cattle were 80% higher than from the dung in untreated cattle. The study speculates that the methane increase may be related to the fact that antibiotics suppress bacteria that compete with methane producing bacteria in the guts of cattle. Another recent study suggested that cud-chewing livestock worldwide, including cattle, account for approximately 4% of greenhouse gas emissions related to human activity.
That is not, however, the only bad news. Methane emissions from cattle manure are estimated to be lower than those from cattle belching. If further studies confirm a connection between antibiotics and greenhouse gas emissions, regulatory actions to limit their use may follow.