Using antibiotics to treat illnesses in livestock could double the level of greenhouse gas emission produced by the animals' wastes, according to a new study.

Researchers at the University of Colorado Boulder discovered that the dung produced by cattle treated with the antibiotic tetracycline emitted higher levels of methane compared with the dung produced by untreated livestock.

Tobin Hammer, one of the authors of the study, said that this could be the first instance where the use of antibiotic treatment on livestock impacted the amount of methane that is released by the animals. The researchers believe the increased gas emission could be caused by the antibiotics altering the microbial competition that goes on inside the intestines of the cows.

Hammer added that if the same increased methane emission occurs whenever the animals belch, then it could be a cause for concern.

Cattle are known to be one of the primary sources of methane, a greenhouse gas that is more potent compared to carbon dioxide.

The gas is produced by gut microbes known as archaea, which are often found thriving in air-free (anaerobic) environments.

Hammer said tetracycline appears to tip the balance of gut microbes within the cattle in favor of these methane-producing microorganisms.

Working with fellow researchers in Finland, Hammer compared the dung of livestock that were given tetracycline with those of cattle that were not given the antibiotic. He then measured the levels of greenhouse gas emitted by the animals' wastes, including carbon dioxide, nitrous oxide and methane.

The researchers found that the antibiotic may have radically changed the activity of the gut microbes, resulting in increased levels of methane.

"The relative abundance of archaea that produce methane increased with antibiotic treatment, and that presumably is why we saw a strong increase in methane emissions," Hammer explained.

Aside from determining the amount of methane emitted by the antibiotic-fed cattle, Hammer and his colleagues also examined how the drug impacts the activity of dung beetles. These creatures are known to help reduce methane levels by oxygenating the animals' wastes and lowering the number of archaea.

While the researchers discovered a change in the microbiota of dung beetles feeding on the dung of tetracycline-fed cattle, they saw that the creatures were still able to help reduce amount of methane produced by the wastes.

However, this was not enough to counter the increased greenhouse gas emission caused by the antibiotic use.

Tetracycline is an antibiotic commonly used by farmers around the world to treat their livestock.

The findings of the University of Colorado Boulder study are featured in the journal Proceedings of the Royal Society B.

Photo: U.S. Department of Agriculture | Flickr

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