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Something to Ruminate On: Low-Methane Sheep

by Diane Wells

I own sheep. After watching them effortlessly leap over the garden gate to munch Swiss chard before nary a hoof has touched, I like to pause and reflect on just what it is I value them for. That wooly coat comes to mind. I also value (and you may think this odd) the historical novel written in their genes. Particularly the Icelandic, whose ancestors accompanied Vikings when they landed on the shores of Iceland nearly 1,200 years ago. Sheep have been around for a long time—roughly 10,000 years—and I like knowing I have such animals roaming the farmstead. It’s estimated hundreds of breeds have been developed over time, and new breeds continue to be added to the mix as animals are selected for their wool, meat, milk and methane. Yes, you read that correctly—methane. Those New Zealand folks that live down under and over have been studying sheep for a long time and for good reason: they have over 38 million of them. That works out to about 12 sheep for every citizen in that country. Over time, they’ve discovered a number of things about the fleet-footed woolies, and one is that some produce less methane than others—a characteristic that could be genetically linked and potentially bred for.

Why do we care about this? Let’s back up a moment and remind ourselves what methane is. We’ve all be reading and hearing about carbon dioxide and the role it’s playing in climate change. What we don’t hear as much about is methane, a greenhouse gas more effective than carbon dioxide (about 21 times more effective according to the U.S. EPA) when it comes to trapping infrared radiation. Although there are natural sources of methane (water bodies, wetlands, permafrost and wildfires), about 60 percent of the methane in the atmosphere was put there by humans. Worldwide, domestic livestock is the number one source of human-related methane production. It’s a byproduct of manure management and anaerobic digestion.

Enter the ruminant

When a ruminant eats, the food slides down the esophagus, slips into the reticulum and sloshes into the rumen. For an adult sheep, this rumen is a 5 to 10-gallon vat that stores, soaks and breaks down food while amylotic and cellulolytic bacteria, protozoa, fungi and bacterial viruses living in the rumen ferment it. It’s this process of fermentation that allows the nutrients contained in grass, hay, browse and silage (my sheep will proudly add broccoli, comfrey, their owner’s best hosta and chives, among other things, to that food list) to be accessible to the animal’s body. The cellulose and starch in fibrous feeds are converted to glucose, which is then broken down into a number of volatile fatty acids: acetic, butyric and propionic. In the process of creating acetic acid, two byproducts are produced: carbon dioxide and methane. The rumen then contracts and forces the gas out. From the animal’s standpoint, burping, belching, eructing, whatever you want to call it, is a good thing. It prevents bloat. From the standpoint of climate methane levels, some folks think this process of releasing methane needs to be tinkered with.

It’s been known for some time now that certain plants produce less methane than others. However, New Zealand researchers at AgResearch (a government-owned research and development company) have recently realized there are individuals that, no matter what you feed them, naturally belch less methane. How do they know this? Sealed breathing chambers. Here’s how it works: a sheep is placed in a cart and wheeled into a chamber where food awaits. The chamber door is then shut, ostensibly “sealing” the animal in. As the animal munches away, oxygen flows into the chamber and the amount of carbon dioxide and methane released is detected and measured. One by one, the research sheep entered the chamber and revealed their methane numbers. Sheep that produced lower levels of methane were separated and put into one flock, while those that produced higher levels of methane were put in a second flock. Both flocks were then fed the same diet over time and gas production was monitored. The researchers discovered the “high-level” sheep produced 8 percent more methane than the “low-level” sheep.

As you can well imagine, there are more than a few remaining unanswered questions. Why does one sheep produce less gas than another? If a sheep produces less methane, does that mean more energy goes towards lamb, wool, meat or milk production? Is this trait heritable and capable of being passed on from generation to generation?

One question I know a number of you are asking is, “Does this issue really deserve all the attention it’s getting?” New Zealanders think so. The methane produced by their 38 million sheep and 10 million cattle accounts for 32 percent of the country’s total greenhouse gas emissions. In 2002, the Pastoral Greenhouse Gas Research Consortium was created for the purpose of developing solutions to reduce those emissions. In August 2009, the New Zealand government vowed it would reduce its 1990 emission levels by 10 to 20 percent by 2020, hence the interest in researching methane production. Their willingness to tackle this issue is admirable.

It is important to note that developing a low-methane sheep breed is not the only avenue they’ve explored. One of the rumen’s microbes directly responsible for methane production has been analyzed and its genome sequenced. The idea is developing a drench or vaccine or adjusting the feed system accordingly could reduce or eliminate that microbe and, consequently, methane production. They’ve also shown that pasture plants containing condensed tannins produce less methane. The tannins also increase milk yields and the rate of weight gain as well as reduce the incidence of bloat and number of parasites. With this knowledge, the options include feeding livestock plants naturally high in the tannins, or adding condensed tannin compounds to usual feeds.

In the United States, ruminant digestion and manure management account for 24 percent and 8 percent of the human-related methane produced, respectively. The majority of methane produced by digestion comes from beef cattle (72 percent) and dairy cattle (23 percent). The remaining 5 percent comes from horses, sheep, swine and goats. Both New Zealand and United States governments have mulled over the idea of levying a tax on ruminants, in an effort to regulate greenhouse gas emissions. So, far there has been strong opposition. Stay tuned for updates.

The author, a brand new contributor to Farming, is a biologist who lives and farms in Vermont’s Northeast Kingdom. Comment or question? Visit www.farmingforumsite.com and join in the discussions.