By Jenny Cade, Biochemistry & Molecular Biology ’15
Eating grass-fed beef and pasture-raised chicken is the eco-friendly thing to do–right? Maybe not, according to a recent paper published in the Proceedings in the National Academy of Science. The study proposes that intensifying livestock production by transitioning from pure grazing to mixed systems–where animals are fed high-energy food like grains–could reduce livestock greenhouse gas emissions by 23% by 2030. Currently, livestock account for 14.5% of all anthropogenic greenhouse gas emissions, so such a reduction would be significant.
In contrast, a comment piece that appeared in Nature last month calls for increasing grazing to make livestock systems more sustainable. Of eight strategies that the authors outline to reduce the environmental and economic costs of raising livestock, “Feed animals less human food” is number one.
Why is there such a stark disagreement? It comes down to the issue of land use. Most of the greenhouse gas emissions caused by livestock comes not from the animals themselves, but from deforestation. Pasture-raised animals require land, and since demands for meat and dairy have been steadily increasing, more and more land has been converted to pasture to raise livestock. In the tropics especially this has led to considerable loss of forests. So, the logic goes, reducing the calories that animals get from grazing by supplementing higher energy feed would reduce the environmental impact of livestock. According to the authors of the PNaS article, “This means that more livestock can be raised on less land, and with fewer emissions per pound of meat or milk produced.”
But growing that feed has an environmental cost too. Feeding animals human food is inherently inefficient in an energy sense, since only a small portion of the calories an animal takes in through food gets converted into calories in its meat. By grazing ruminants–animals like cattle, sheep, and goats that can digest tough fibers that are inedible to humans–we can gain access to more calories.
It doesn’t seem like we’ve found the perfect system for sustainable livestock yet. There are too many factors–not just greenhouse gas emissions and land use, but pollution caused by animal waste, water use, food security, and of course economic sustainability. The good news is that there’s plenty of work being done by researchers and farmers who want to help find solutions.
In the meantime, should we go for grass-fed or grain-fed? I find the grazing argument more convincing, but you’ll have to read the articles to decide for yourself. One thing that the authors of both papers agree on: the impact on the environment would be lower if we all ate less meat and dairy.
Read the original articles:
http://www.pnas.org/content/111/10/3709
P. Havlik, H. Valin, M. Herrero, M. Obersteiner, E. Schmid, et al. Climate change mitigation through livestock system transitions. Proceedings of the National Academy of Sciences, 2014; DOI: 10.1073/pnas.1308044111
“Better livestock diets to combat climate change, improve food security” (press release)
Mark C. Eisler, Michael R. F. Lee, John F. Tarlton, Graeme B. Martin, John Beddington, et al. Agriculture: Steps to sustainable livestock. Nature, 2014; DOI: 10.1038/507032a
Listen to an interview with two of the authors on the Nature podcast.
Photo: Mark J Sebastian