Dr David Pacheco in front of a line of respiration chambers at the Palmerston North AgReserach campus (Alex Braae)

Can new crops crack down on cow methane? Meet the scientists finding out

The debate about methane emissions from farming is both ongoing and polarising, and many are pinning their hopes on scientific advances to avoid both de-stocking and climate breakdown. But how effective can these measures actually be? Alex Braae visited a research lab on the front lines of this fight. 

At a sprawling campus on the outskirts of Palmerston North, research is taking place that could shape the future of New Zealand’s rural economy. 

It is here that the grasslands facility of crown research entity AgResearch is based. And it is here where one of the most important scientific questions in the country is being thrashed out – can science help meaningfully lower the methane emissions of cows and sheep? 

The figures for how much it matters are vast. Dairy exports alone are now worth around $19 billion a year, not to mention beef, lamb and wool exports. The money that flows from that ends up effectively propping up scores of towns across the country, along with the vast network of economic activity that takes place around them. 

But the emissions profile is also vast, and growing. Cows and sheep, as ruminants, put a lot of methane into the world. There are more than six million cows currently munching away on New Zealand pasture, and tens of millions of sheep. Overall, the digestion process of livestock contributes to about a third of the country’s gross emissions, on top of the other emissions attached to farming, including but not limited to shipping the product to where it needs to be. And the share is high in part because methane has a much sharper (but shorter) climate impact. 

So what on earth can be done about it? Destocking isn’t an answer that will satisfy those who economically rely on farming, and besides, in the hierarchy of human activities that create emissions, producing food is a pretty important one to keep going with. Under the Zero Carbon Act, there are targets to reduce biological methane by 10% on 2017 levels by 2030, and between 24% and 47% by 2050. 

Enter Dr David Pacheco, who leads AgResearch’s Animal Nutrition & Physiology team. One of his primary jobs right now is to find out exactly what farmers should be feeding their animals, so that they don’t burp out so much methane. 

Dr David Pacheco pointing out a piece of testing equipment in the AgResearch lab (Alex Braae)

One area that has shown particular promise is the use of brassica crops. This group of crops include kale and swedes among others, but it is forage rape, a leafy brassica crop, that got the team’s attention. “When you feed one unit of ryegrass [the grass that is typically seen on farms] or one unit of forage rape, you get about 25% less methane from sheep and cattle fed with the forage rape,” says Pacheco. So, problem solved? 

Not so fast, he warns. “The way that brassica crops are used in practice means high animal densities, and you start getting increases in nitrous oxide. Because of the high densities you get a lot of pugging in soils, and because the crop is commonly used in winter, you also have very wet soils. Those are conditions where the amount of nitrous oxide from urine increases.” That’s not necessarily a workable trade-off either, because nitrous oxide is itself a greenhouse gas, along with the animal welfare concerns that often arise from this sort of high-density farming, with cows quite literally getting stuck in the mud. 

A major part of the work of AgResearch is therefore about understanding what these trade-offs will mean for a total farming system. Cropping requires heavier cultivation of the soil too, and the soil disturbance created by that releases carbon. Dr Pacheco’s colleagues have done analysis that takes into account all these elements and found that use of forage rape would result in an a total emissions reduction of 1-3% in practice.  

The key then becomes understanding why the brassica works so well to reduce methane, and then apply those lessons to minimise the risks of the trade-offs. “Methane is one side of the equation, but we also research the aspects related to nitrogen utilisation by the animals eating different feeds. Working in the two areas actually helps a bit, because I feel I don’t necessarily lose track of one or the other, they’re all linked.” 

Cows in deep mud after winter grazing went wrong (Image: Radio NZ/Supplied)

The experiments to figure this out begin in a lab that smells a bit like a hospital where a cow has got loose. In this room, there’s an escalating series of tests that take place to study potential tools to reduce the production of methane in the rumen, which is the part of the cow’s digestive tract where the microbes that produce methane live. The lab has different equipment that simulates what happens in the rumen. Using these simulations, the research team studies feeds or novel compounds to see what will show promise, and which paths will be dead ends. The first machine can test 96 compounds in the space of five hours. Scientists put them in small glass jars and then place those jars in an incubator set to the temperature of a cow’s stomach, which gently rocks them to simulate digestion. 

The gases that come out of this process tell the scientists a simple “yes” or “no” regarding whether greenhouse gas production has been reduced. For those options that show promise, they can be put through longer term tests that take 48 hours, and include additional inputs. In this system, the researchers also gather insights about digestion – if the feed does not digest properly, it is not a good option for feeding cows and sheep, even if methane is reduced. 

And if the researchers want to understand medium-term effects of any promising feeds or compounds, there’s a further three-week test to go through, to ensure that the results still apply over the longer term. Pacheco says there’s a simple mentality that guides the work of AgResearch’s scientists – “if we see a good result, we ask, is this for real?” 

It is only at this point, when there have been tests to determine both the usefulness of the option, and that it won’t cause harm, that any of these compounds get anywhere near an actual animal. This takes place in a much larger and meatier-smelling room on the other side of the campus.  

Here, a long row of metal boxes called respiration chambers have been set up. When a really promising option needs to be tested, sheep and cows are herded into them, and given something new to eat. The emissions that they produce are closely monitored, so that a much clearer picture can emerge of what a feed can do in terms of reducing methane. 

Isn’t this sort of process terrifying for the animals? Pacheco concedes that it could cause them some discomfort, but steps are taken to minimise that. They can see out the sides of their containers, which means that other members of their herd are always visible. “We know we’re putting animals through some inconvenience, so we try and do it in as respectful a way as possible,” he says.

Many people and organisations eagerly await the results that come out of AgResearch. Over and above individual farmers, organisations like Fonterra keep in close contact – they even have an office of their own on the Palmerston North campus. AgResearch is partly funded by the government, and partly funded by industry organisations like Fonterra and Beef+Lamb. The work can also help advance the global scientific community’s understanding of the issues. 

Many of the options found end up being a case of two steps forward, and one step back. But despite these challenges, Pacheco is confident that his team’s work will give farmers solutions, and that they’ll then be picked up by the industry. He doesn’t think that there will be one solution – rather it’s about finding a combination of approaches that give the best results. 

“Every little bit we do counts,” he says. “The conversations I have with farmers – they really know what’s going on, and they really want to do something positive for the environment.” 

Travel costs for this article were partially funded by the Aotearoa Science Journalism Fund



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