Sheep and Other Livestock May Not Produce Methane Equally: Source of Greenhouse Gases

Livestock may be having a major impact on our climate. It turns out that a whopping total of one-fifth of methane emissions can be attributed to livestock such as cattle, sheep and other ruminants. As greenhouse gases continue to increase, farmers may want to think which livestock they raise in the future.

According to the Intergovernmental Panel on Climate Change (IPCC), levels of carbon dioxide, methane and nitrous oxide are increasing at a rapid rate. In fact, the atmospheric concentration of methane, which is about 28 times more potent than carbon dioxide, has been increasing since the 18^th century and has now increased by 50 percent compared to pre-industrial levels. That's why researchers wanted to take a closer look at what animals produce more methane in an effort to potentially curtail emissions.

"We wanted to understand why some sheep produce a lot and some produce little methane," said Eddy Rubin, one of the researchers, in a news release. "The study shows that it is purely the microbiota responsible for the difference."

In order to figure out why the amount of methane that ruminants produce varies, the researchers measured methane yields from a cohort of 22 sheep. From this group, they selected four sheep with the lowest methane emissions, four with the highest and two with intermediate emission levels. The scientists then collected rumen metagenome DNA samples in order to learn a bit more about them.

So what did they find? The scientists found a methane-producing pathway and three variants of a gene encoding an important methane-forming reaction that were involved in elevated methane yields. In fact, the expression levels of genes involved in methane produced varied substantially across sheep, which suggested differential gene regulation might be the cause of methane production.

"It's not so much the actual composition of the microbiome that determines emissions-which conventional wisdom would suggest-but mostly transcriptional regulation within the existing microbes that makes the difference, which is a concept that is relatively new in metagenomic studies," said Rubin in a news release.

The findings could mean that it might be possible to incorporate low-emission livestock into herds and thus help lower greenhouse gas emissions in our atmosphere.

The findings are published in the journal Genome Research.