Whenever I come across cows here in the southwest of the UK, usually placidly munching on a mouthful of grass, they always seem too lovable to be villains. But as we face growing twin challenges of feeding the world and fighting climate change, they’re increasingly getting a bad reputation.
Some scientists highlight reducing how much beef we eat, in particular, as an important step towards future sustainability. They say only about three or four parts in 100 of the energy in livestock feed becomes our food, while the rest is lost as manure, heat, digestive gases and slaughter by-products. Switching to more intensively farmed chicken or pork and plant-based food would be more efficient, the argument goes. It also gives a greater chance to trap carbon from waste material, which might otherwise become planet-warming greenhouse gases, as biochar that can help improve soil fertility.
A couple of years back I put this to Peter and Henri Greig who run my favourite local butchers, Pipers Farm. As they showed us round their farm Peter explained how their Red Ruby cattle can graze Devon moorland that can’t be used for crops, before moving on to pasture. While I still don’t eat a lot of beef for both environmental and health reasons, that seems a good reason for not demonising cows entirely. In fact, a paper in the June 2014 issue of the Journal of Dairy Science highlights previous research that found more grazing land exists, unusable for human food, than cropping land.
We can’t ignore what that promises for feeding the world in the future, but we can’t ignore cows’ greenhouse gas emissions either. However, rather than beef cattle, the new paper’s authors focussed on reducing levels of the potent greenhouse gas methane coming out of the digestive systems of dairy cattle. Joanne Knapp, a consultant who has researched nutrition in ruminant animals like cattle, told me her team’s interest comes in part thanks to its backers: Innovation Center for US Dairy.
Given that the Innovation Center’s stated aim starts ‘To increase demand for dairy products and ingredients globally’, the team’s motivation isn’t a surprise. “There’s a lot of emphasis on the burden from ruminant animals in terms of methane,” Joanne says. “The proportion of impact from dairy cattle and expectations on what can be done to mitigate that are sometimes overblown. However, we’ve shown that there are lots of different avenues to reducing emissions that already exist and can be combined.”
Around 22% of greenhouse gases resulting from human activity are linked to farming. But Joanne’s team emphasises that land use change, for example where forests are turned to farmland, is the largest part, responsible for around 15% of all human-caused emissions. The researchers also say dairy farming is responsible for little land use change, and that less than 2% of all human-caused emissions are thought to come from dairy animals.
Although I was attracted to Joanne’s team’s research partly because of the opportunity for fart jokes, the methane cows produce is mostly not from farting. More of it comes out of their mouth, but even that’s not strictly burping, she stressed. Instead, thanks to how their four-stomached digestive system works, they simply breathe it out. Yet the impact of this natural process is no joke. Gas from the guts of livestock is responsible for 17% of all ‘human-emitted’ methane, and 3.3% of our total greenhouse gas emissions.
Our understanding of cows’ digestion therefore played a key part in several of the existing approaches to cutting methane emissions that Joanne’s team reviewed. Methane is produced as a by-product as microbes help ferment and, therefore, quickly break down plant matter in cows’ stomachs. Giving carefully balanced amounts of conventional feeds can control this biochemical pathway, to minimise methane and maximise milk production.
Other strategies include adding ‘rumen modifier’ substances to feed that suppress methane production, or trying to reduce the number of these ‘methanogen’ microbes. However these approaches aren’t straightforward as they can slow fermentation, and there are always other microbes ready to adapt and fill any newly-vacated niches.
Joanne’s team also focussed on other ways to boost the amount of milk produced by each cow, either by breeding or better care. One of the most important aspects of this idea was working to get cows producing milk for longer, starting them earlier and improving their health. “Total [methane] emissions will be decreased if annual production of milk remains constant and fewer cows are needed to produce the same amount of milk,” they wrote. In the UK, around a quarter of the methane produced by dairy cattle herds comes from replacement livestock.
Yet they didn’t consider one method for reducing methane emissions that has attracted media attention – inflatable backpacks attached to cows that collect their digestive gases. Though Joanne acknowledged the Argentinian scientists who’d developed them have made useful research findings, she’s sceptical about their broader usefulness. “Equipment like that to collect methane from animals will be more expensive to make and maintain than what you’d make in return,” she said. “In the US there are nine million dairy cattle, nine million replacement heifers, and ninety million beef cows. Who’s going to maintain the equipment? Argentina’s much the same.”
Overall, Joanne’s team’s review makes the conservative estimate that combining these strategies can cut methane released per kilogram of milk by 15-30%. Europe and North America already exploit their potential, with intensive farming giving around five times as much milk for the amount of methane produced than more extensive approaches. “In India a cow produces 700kg of milk per year,” Joanne explained. “In Europe and North America, it produces 10,000kg. That’s where a lot of the environmental difference is. You can significantly decrease the impact of these animals when they’re more productive.”
Not cowed by limited support
The direct financial benefit from better productivity is the main reason for farmers taking these steps, Joanne stressed, as other support for cutting emissions is scarce. “I’ve been working in this area for 25 years,” she recalled. “When I started out of university a lot of work was with the US Environmental Protection Agency, and I asked why they didn’t put money into it. There are now funds for capturing methane from manure, as the systems needed for that cost $80,000-$100,000.”
However carbon trading schemes in the US are beginning to help, Joanne added. “I’ve seen the annual budgets for some operations where they’re collecting methane from waste and manure,” she revealed. “If it were not for the carbon trading income those operations wouldn’t be financially solvent. Dairy farmers who do implement measures to reduce methane are getting credit for it. It hasn’t been an overwhelming burden.”
Yet we shouldn’t become complacent, as the Food and Agriculture Organization of the United Nations expects global dairy demand to be 58% higher by 2050 than it was in 2011. A quick calculation suggests that in that case methane produced per kilogram of milk would have to fall by 47% for overall dairy emissions to stay the same. That’s clearly more than Joanne’s team’s conservative estimate for possible reductions with existing methods. However, the consultant asserted that estimates they’ve worked on elsewhere show that a ‘very feasible’ 75% increase in milk production per cow could meet the 2050 target. It would do so with 11% fewer cows and the same methane emissions, manure excretion, and water usage as in 2010, she added.
Humans have farmed cows for around 10,500 years, long enough for the two species to shape each other’s development. To me, our society’s dependence on cows is comparable to its dependence on fossil fuels, and therefore changing our relationship with them could be similarly difficult. And while Joanne’s confident that the dairy industry can already make significant emissions cuts, she stressed that governments must ultimately ensure any actions are adequate. “A comprehensive review like ours will guide policy,” she underlined. “The industry is already implementing many approaches to reducing its environmental impact. Agriculture has been an easy target because there are benefits to profitability and productivity. It looks like a win-win-win and policies should be directed to that.”
Knapp, J., Laur, G., Vadas, P., Weiss, W., & Tricarico, J. (2014). Invited review: Enteric methane in dairy cattle production: Quantifying the opportunities and impact of reducing emissions Journal of Dairy Science, 97 (6), 3231-3261 DOI: 10.3168/jds.2013-7234