Cow Versus Chicken: The True Carbon ‘Hoofprint’ of Livestock
We know that raising farm animals as part of the food production system contributes markedly to green house gas emissions, also known as a ‘carbon hoofprint.’ But is there a difference between the impact on climate between different countries? Which animals are leaving the greatest mark on our environment and climate?
The newest paper to be published in the Proceedings of the National Academy of Sciences (PNAS) investigates the answers, providing a comprehensive assessment of what cows, sheep, pigs, poultry and other farm animals are eating in different parts of the world. The study also analysed how efficiently they convert that feed into milk, eggs and meat, and the amount of greenhouse gases they produce.
Scientists say the new data fill a critical gap in research on the interactions between livestock and natural resources region by region.
“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,” said Harvard University’s William C. Clark, editorial board member of the Sustainability Science section at PNAS.
Poor Versus Wealthy
The study found a significant increase in the amount of food needed to produce one kilogram of protein for animals in the developing world as opposed to animals in wealthy countries.
To do so, the researchers broke down livestock production into nine global regions—the more developed regions of Europe and Russia, North America and Oceania, along with the developing regions of Southeast Asia, Eastern Asia (including China), South Asia, Latin America and the Caribbean, sub-Saharan Africa, and the Middle East and North Africa.
It was found that in arid regions of sub-Saharan Africa, for example, the food available to grazing animals contained far fewer nutrients than that in other regions. Therefore, cows were consuming up to ten times more feed—mainly in the form of rangeland grasses—to produce one kilogram of protein than a cow kept in more favorable conditions.
Subsequently, the developing world were found to account for the most emissions from livestock, including 75 percent of emissions from cattle and other ruminants and 56 percent from poultry and pigs. However, we have to interpret these findings with caution as the numbers do not include emissions from the food production system as a whole, but rather just the animal.
“While our measurements may make a certain type of livestock production appear inefficient, that production system may be the most environmentally sustainable, as well as the most equitable way of using that particular land,” said Philip Thornton, co-author of the study.
The amount of greenhouse gases released for every kilogram of protein produced is known as “emission intensity.” In this study, scientists modelled only the emissions linked directly to animals—the gases released through their digestion and manure production. Naturally, gas emissions vary widely depending on the animal involved and the quality of its diet.
Cattle (for beef or dairy) are the largest contributors of greenhouse emissions from livestock worldwide, accounting for a whopping 77 percent of the total. Pork and poultry (monogastrics) account for just 10 percent of emissions.
The authors speculate that the driver behind the low emissions of the monogastrics industries are the large industrial systems in place. These systems have additional carbon costs not factored into the numbers above — notably greenhouse gases produced by the energy and transport services, as well as the felling of forests to grow crops for animal feed. The industrial system used by the cattle industry seems to be overlooked.
For scientists, the most important insights emerging from the new data relate to the amount of feed livestock eat to produce per one kilogram of protein, known as “feed efficiency.”
The study shows that ruminant animals (cows, sheep and goats) require up to five times more feed to produce one kilogram of protein in the form of meat than one kilogram of protein in the form of milk.
“The large differences in efficiencies in the production of different livestock foods warrant considerable attention,” the authors note. “Knowing these differences can help us define sustainable and culturally appropriate levels of consumption of milk, meat and eggs.”
Cow Versus Chicken
Comparing carbon costs of livestock globally, poultry produced 3.7 kilograms of carbon per kilogram of protein, and pork produced 24 kilograms of carbon per kilogram of protein. Now compare this to ruminants, which produced anywhere from 58 to 1,000 kilograms of carbon per kilogram of protein.
The study confirmed that pigs and poultry are far more efficient at converting feed into protein than are cattle, sheep and goats, and this is the case regardless of which country the animals are raised.
Considering the carbon hoofprint of different animals, as well as the amount of land and resources required to produce an animal’s feed, it’s become very clear which livestock are favourable in terms of sustainability.
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