Environmental concerns about animal manure.

The structure of swine production has changed dramatically in the last four decades. Raw materials for swine feeds are often grown in regions other than where swine production takes place. Swine manure is mostly spread in the neighborhood of the facilities, which may lead to soil accumulation of minerals such as P, Cu, and Zn. Moreover, soil nitrate may leach and result in enhanced nitrate levels in ground and surface water. Large swine units generate odors, ammonia, and dust that can exceed tolerable levels. Negative effects of swine production on the environment have already led to new legislation that limits the use of animal manure or the expansion or localization of pig operations in some countries. The consequences of intensive swine production on the environment and possible solutions by means of nutrition are outlined. Also, discussed are experiences from the Dutch situation, forthcoming legislation, and environmental constraints on pig production in the future. Our approach centers more on the system level.