Multiple forces have disturbed traditional pastorialists' ecologically sound livestock systems, leaving herders to crowd with their animals in areas where the land is quickly laid to waste. Complex economic and social forces lead to mismanagement of herds, causing extensive and sometimes irreversible degradation of drylands and destruction of forests. In countries such as Botswana, cattle are esteemed not just for monetary reasons, but as a yardstick of social prestige. In India, Hinduism preaches a reverence for cows that, together with the animals' economic value to poor households, helps account for the world's largest cattle population. Worldwide, larger livestocks populations emit the potent greenhouse gas methane into the atmosphere, contributing to climate change.
Cattle can overgraze perennial grasses, allowing annual weeds and tougher shrubs to spread.
The new weeds anchor the topsoil poorly, and can leave it vulnerable to trampling hooves and wind erosion. Under persistent grazing, the bare ground becomes impermeable to rainwater, which then courses off the surface, carrying away topsoil and scouring stream beds into deep gullies. Subsidies sometimes affect the total scale of livestock production unsubstantially, but greatly magnify its environmental impact. Including fuel for powering farm machinery and for manufacturing fertilizers and pesticides, feed grain turns out to be an energy-intensive product. All told, almost half of the energy used in American agriculture goes into the livestock sector, and producing the red meat and poultry eaten each year by a typical American uses the equivalent of 190 liters of gasoline.