the evolution of Bos indicus in the Indian subcontinent. There is a possible third domestication event 8,500 years ago, with a potential third species Bos africanus arising in Africa. In the United States, the growth of the beef business was largely due to expansion in the Southwest. Upon the acquisition of grasslands through the Mexican–American War of 1848, and later the expulsion of the Plains Indians from this region and the Midwest, the American livestock industry began, starting primarily with the taming of wild longhorn cattle. Chicago and New York City were the first to benefit from these developments in their stockyards and in their meat markets. Production Beef cattle are raised and fed using a variety of methods, including feedlots, free range, ranching, backgrounding and intensive animal farming. Concentrated Animal Feeding Operations (CAFOs), commonly referred to as factory farms, are commonly used to meet the demand of beef production. CAFOs supply 70.4% of cows in the US market and 99% of all meat in the United States supply. Cattle CAFOs can also be a source of E. coli contamination in the food supply due to the prevalence of manure in CAFOs. These E. coli contaminations include one strain, E. coli O157:H7, which can be toxic to humans, because cattle typically hold this strain in their digestive system. Another consequence of unsanitary conditions created by high-density confinement systems is increased use of antibiotics in order to prevent illness. An analysis of FDA sales data by the Natural Resources Defense Council found 42% of medically important antibiotic use in the U.S. was on cattle, posing concerns about the development of antibiotic resistant bacteria. Environmental impact The consumption of beef poses numerous threats to the natural environment. Of all agricultural products, beef requires some of the most land and water, and its production results in the greatest amount of greenhouse gas emissions (GHG), air pollution, and water pollution. A 2021 study added up GHG emissions from the entire lifecycle, including production, transportation, and consumption, and estimated that beef contributed about 4 billion tonnes (9%) of anthropogenic greenhouse gases in 2010. Cattle populations graze around 26% of all land on Earth, not including the large agricultural fields that are used to grow cattle feed. According to FAO, "Ranching-induced deforestation is one of the main causes of loss of some unique plant and animal species in the tropical rainforests of Central and South America