In East Asia, says Steinfeld, increased animal density near urban centers now results in unparalleled waste loads, with the capacity of plants to use nutrients from manure sometimes exceeded by 1,000 kilograms of nitrogen per hectare, which poses risks to flora and fauna and ultimately to humans. Manure also produces greenhouse gases 16 percent of annual methane emissions and 7 percent of the more aggressive nitrous oxide that cause global climate change. Robbin Marks, senior resource specialist at NRDC, points to the large corporate farms that dominate livestock production as the culprits that create pollution problems when their enormous manure storage sites contaminate bodies of water and release toxic fumes into the air. Tightening regulations, involving communities in decisions about setting up factory farms, and banning manure runoff and open-air cesspools are some of the solutions Marks proposes. The U.S. Department of Agriculture and the Environmental Protection Agency are now drafting a strategy to limit these problems.
Livestock can improve environmental quality when used in traditional farming systems.
De Vries says that ownership of livestock is a great motivation for farmers to plant forage bearing trees and shrubs, grass contours, and pasture, all of which help to control erosion and conserve water. But without proper training and incentives for smallholders, livestock can damage the environment, especially through overgrazing on open rangeland. There are too many people raising too many animals in the low-rainfall areas in West Asia and North Africa, says Hazell. The encroachment of cropping further erodes the soil in these lands, some of which are already drought-prone. He believes livestock production should rely less on grazing systems and more on intensive production in higher-potential areas.