AN analysis of greenhouse gas (GHG) emissions related to global livestock systems, published Dec. 16 in Proceedings of the National Academy of Science (PNAS), shows vast differences in animal diets and emissions.
The resources required to raise livestock and the impact farm animals have on the environment 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 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 GHGs they produce.
The study, produced by scientists at the International Livestock Research Institute (ILRI) in Kenya, the Commonwealth Scientific & Industrial Research Organization (CSIRO) in Australia and the International Institute for Applied Systems Analysis (IIASA) in Austria, found 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 found that pork and poultry are being produced far more efficiently than milk and beef, and GHG 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 lead author of the study Mario Herrero, formerly of ILRI and currently 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.
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.
By the numbers
The study divides livestock production into nine global regions: the more developed regions of (1) Europe and Russia, (2) North America and (3) Oceania, along with the developing regions of (4) Southeast Asia, (5) Eastern Asia, including China, (6) South Asia, (7) Latin America and the Caribbean, (8) sub-Saharan Africa and (9) the Middle East and North Africa.
The data reveal sharp contrasts in overall livestock production and diets, the researchers said. For example, of the 59 million tons of beef produced in the world in 2000, the vast majority came from cattle in Latin America, Europe and North America. All of sub-Saharan Africa produced only about 3 million tons of beef.
Highly intensive, industrial-scale production accounts for almost all of the poultry and pork produced in Europe, North America and China, the researchers reported, while between 40% and 70% of all poultry and pork production in South and Southeast Asia, the Middle East and Africa is produced by small-scale farmers.
The researchers also calculated the amount of GHGs livestock are releasing into the atmosphere and examined emissions by region, animal type and animal product. They modelled only the emissions linked directly to animals — the gases released through their digestion and manure production.
According to ILRI, some important findings include:
* South Asia, Latin America, Europe and sub-Saharan Africa have the highest total regional emissions from livestock. Between the developed and developing worlds, the developing world accounts for the most emissions from livestock, including 75% of emissions from cattle and other ruminants and 56% from poultry and pigs.
* Cattle (beef or dairy) are the biggest source of GHG emissions from livestock globally, accounting for 77% of the total. Pork and poultry account for only 10% of emissions.
The researchers noted that some of the most important insights and questions emerging from the new data relate to the amount of feed livestock consume to produce 1 kg of protein — i.e., feed efficiency — and the amount of GHGs released for every kilogram of protein produced, which is known as "emission intensity."
The study found that cows, sheep and goats require up to five times more feed to produce 1 kg of protein in the form of meat than 1 kg of protein in the form of milk.
Globally, pork produced 24 kg of carbon per kilogram of edible protein, and poultry produced only 3.7 kg of carbon per kilogram of protein, compared with anywhere from 58 to 1,000 kg of carbon per kilogram of protein from ruminant meat.
The researchers cautioned that the lower emission intensities in the pig and poultry sectors are driven largely by industrial systems, "which provide high-quality, balanced concentrate diets for animals of high genetic potential."
While the new data will greatly help assess the sustainability of different livestock production systems, the researchers cautioned against using any single measurement as an absolute indicator of sustainability.