In a way, our love of wool is the heart of the dilemma. If we continue to keep all of these sheep around—just over a billion head worldwide at last count—the opportunities for sweaters go down because the methane produced by sheep and other delicious and useful ruminants, the class of mammal that processes food through fermentation, accounts for over a quarter of global methane emissions from human-related activities. And methane is the second most prevalent greenhouse gas in the United States.
While sheep herds overall still have nothing on cattle-related emissions, in the largely sheep-dependent economy of New Zealand, livestock emissions account for a full third of the country's greenhouse gases.
But researchers from these two nations are grabbing the dilemma by the horns—taking it on like a ram takes on a drone—by investigating the microbes that live in the part of sheep stomachs that gives the ruminant classification its name, the rumen. Methane is produced there by microbes called methanogens.
Teams from New Zealand's AgResearch institute and the US Department of Energy's Joint Genome Institute have just published a study in the journal Genome Research on the genetic make-up of high methane-emitting and low methane-emitting sheep and their methanogens. The results indicate that we may be able to breed a low-emission flock.
The team measured methane yields from 22 sheep, including the economically important Romney, Perendale, and Corriedale breeds, among others. While measuring methane yields might sound labor intensive in the worst way, the study's lead author, Dr. Graeme Attwood made it sound easy, or at least easier than following sheep butts around.
"We measured the methane emissions in respiration chambers which is basically a perspex box in which the animals are kept, and gas inflow and gas outflow are measured accurately," he said via email from New Zealand. "We also measure the amount of feed eaten over the same period, then express the amount of methane emitted per kilogram of dry matter feed eaten, which is known as methane yield."
The researchers then sequenced the rumen microbiome metagenome (the DNA) and metatranscriptome (RNA) and were able to identify a "discrete set of rumen methanogen," that correlated with methane yields.
"Understanding the microbial composition of a low methane animal and how its rumen works, will enable us to focus on targeting the methanogens directly using complementary approaches such as drenches, slow release boluses or specialized forages and supplements," Attwood said in a separate statement.
This understanding also allows for selective breeding, not for thick wool or heavy body weights (which is how these breeds came to be in the first place), but for low-emissions.
Our livestock troubles are deeper than wool, of course. A recent study that looked how our diets relate to the changing climate basically admitted that the rate at which Americans, and increasingly the rest of the world, eat meat isn't sustainable, for reasons beyond just the greenhouse gases, although that's definitely part of the problem.
"The average efficiency of livestock converting plant feed to meat is less than 3 percent, and as we eat more meat, more arable cultivation is turned over to producing feedstock for animals that provide meat for humans," Bojana Bajzelj, an engineering professor at University of Cambridge, said.
"The losses at each stage are large," he explained, "and as humans globally eat more and more meat, conversion from plants to food becomes less and less efficient, driving agricultural expansion and land cover conversion, and releasing more greenhouse gases."
The inefficiencies will remain, but then, the researchers admit, so will meat consumption, to say nothing of wool. In fact, with an unstable climate unleashing polar vortices, we may need it more than ever—but it's nice to imagine that the bucolic image of sheep on a hillside could fit into a more responsible vision of the future.