A new study published Tuesday in the Proceedings of the Royal Society B reported that treating cattle with the antibiotic tetracycline for only three days increased the amount of methane generated in their manure by 80 percent. The research team said the boost may be due to an increase in archaea, which are methane-producing microorganisms, in the digestive systems of treated cattle. This increase is caused by the antibiotics suppressing other bacteria.
Methane is a potent global warming gas related to climate change. The team wrote, “To the best of our knowledge, this is the first report of antibiotics increasing methane emissions.”
These findings are the first that have noted an increase in greenhouse gas emissions due to the use of antibiotics in cattle. A separate study suggested that as much as 4 percent of the world’s greenhouse gas emissions that are related to human activity are a result of methane emissions from cud-chewing livestock.
Antibiotics make animals grow bigger and faster. Farmers have been asked to stop giving their livestock so many of them, out of concerns that the practice may be a factor in the increase in antibiotic-resistant “superbugs.”
Todd Hammer, from the University of Colorado at Boulder, helped conduct the study and said the team was already well aware of the negative consequences of antibiotic use in animals, but, “this was a pretty unexpected link between antibiotics and this other important environmental issue that we care about – greenhouse gases.”
The gust of all mammals, including people, are full of microbes that help with the digestion of food. These microbes include not only archaea, but also fungi and bacteria. However, archaea can produce a lot of methane. The team wrote, “We propose that by specifically suppressing bacteria in the gust and subsequently in dung, antibiotic treatment enables methanogens to outcompete bacteria for hydrogen, increasing their concomitant methane output.”
The researchers suggest that future studies should look at antibiotics’ effect on cow belches, which create less methane than farts.