cycling of carbon through the biogenic carbon cycle. In 2010, enteric fermentation accounted for 43% of the total greenhouse gas emissions from all agricultural activity in the world, 26% of the total greenhouse gas emissions from agricultural activity in the U.S., and 22% of the total U.S. methane emissions. The meat from domestically raised ruminants has a higher carbon equivalent footprint than other meats or vegetarian sources of protein based on a global meta-analysis of lifecycle assessment studies. Methane production by meat animals, principally ruminants, is estimated 15–20% global production of methane, unless the animals were hunted in the wild. The current U.S. domestic beef and dairy cattle population is around 90 million head, approximately 50% higher than the peak wild population of American bison of 60 million head in the 1700s, which primarily roamed the part of North America that now makes up the United States. See also Monogastric Pseudoruminant References External links Digestive Physiology of Herbivores – Colorado State University (Last updated on 13 July 2006) Britannica, The Editors of Encyclopaedia. "Ruminant". Encyclopædia Britannica, Invalid Date, https://www.britannica.com/animal/ruminant. Accessed 22 February 2021. Extant Ypresian first appearances Cetruminantia