a1 Assistant Professor of Agricultural Education and Studies and Animal Science, Iowa State University, Ames, IA 50011.
The nutrient composition of swine excreta can be altered by manipulating the composition of the pig's diet Several approaches are reviewed: feeding according to the pig's growth phase, formulation according to the feed's digestible amino acids, use of crystalline amino acids, the ideal protein approach, formulation according to available phosphorus, and the addition ofphytase enzymes. Each has the potential to lower nitrogen or phosphorus excretion levels. Together they can dramatically reduce the nitrogen and phosphorus concentration of swine manure, which could be a major advantage in regions with a high density of swine or for swine operations with limited access to arable land. However, the value of the swine manure would be much less as a fertilizer because these two elements are important plant nutrients.