New study cites livestock efficiency in GHG emissions

PNAS study cites livestock type and production, feed sources and geography in greenhouse gas emissions.

Yet another detailed analysis of greenhouse gas (GHG) emissions related to global livestock systems, published Dec. 16 in the Proceedings of the National Academy of Science (PNAS), shows vast differences in animal diets and emissions.

The resources required to raise livestock and the impacts of farm animals on environments vary dramatically depending on the animal, the type of food it provides, the kind of feed it consumes and where it lives, according to the study, which offers the a detailed portrait of "livestock ecosystems" in different parts of the world.

The study is the newest comprehensive assessment assembled of what cows, sheep, pigs, poultry and other farm animals are eating in different parts of the world; how efficiently they convert that feed into milk, eggs and meat, and the amount of greenhouse gases they produce.

The study, produced by scientists at the International Livestock Research Institute (ILRI) in Kenya, the Commonwealth Scientific & Industrial Research Organisation (CSIRO) in Australia and the International Institute for Applied Systems Analysis (IIASA) in Austria, shows that animals in many parts of the developing world require far more food to produce 1 kg of protein than animals in wealthy countries.

It also shows that pork and poultry are being produced far more efficiently than milk and beef, and greenhouse gas emissions vary widely depending on the animal involved and the quality of its diet.

"There's been a lot of research focused on the challenges livestock present at the global level, but if the problems are global, the solutions are almost all local and very situation-specific," said Mario Herrero, lead author of the study who earlier this year left ILRI to take up the position of chief research scientist at CSIRO.

"Our goal is to provide the data needed so that the debate over the role of livestock in our diets and our environments and the search for solutions to the challenges they present can be informed by the vastly different ways people around the world raise animals," Herrero said.

"This very important research should provide a new foundation for addressing the sustainable development of livestock in a very resource-challenged and hungry world, where, in many areas, livestock can be crucial to food security," added Harvard University's William C. Clark, editorial board member of the Sustainability Science section at PNAS.

For the last four years, Herrero has been working with scientists at ILRI and IIASA to deconstruct livestock impacts beyond what they view as broad and incomplete representations of the livestock sector. Their findings — supplemented with 50 illustrative maps and more than 100 pages of additional data — anchor a special edition of PNAS devoted to exploring livestock-related issues and global change.

The series of PNAS articles can be found at

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