Animal management to reduce phosphorus losses to the environment

ABSTRACT Water quality in the United States is threatened by contamination with nutrients, primarily nitrogen and phosphorus. Animal manure can be a valuable resource for farmers, providing nutrients, improving soil structure, and increasing vegetative cover to decrease erosion potential. At the same time, application of manure nutrients in excess of crop requirements can result in environmental contamination. Environmental concerns with P are primarily associated with pollution of surface water (streams, lakes, rivers). This pollution may be caused by runoff of P when application to land is in excess of crop requirements. Increased specialization and concentration of livestock and crop production has led to the net export of nutrients from major crop-producing areas of the country to areas with a high concentration of animal agriculture. Concentrated animal agriculture has been identified as a significant source of P contamination of surface water. Areas facing the dilemma of an economically important livestock industry concentrated in an environmentally sensitive area have few options. If agricultural practices continue as they have in the past, continued damage to water resources and a loss of fishing and recreational activity are inevitable. If agricultural productivity is decreased, however, the maintenance of a stable farm economy, a viable rural economy, and a reliable domestic food supply are seriously threatened. Decreasing the P content of manure through nutrition is a powerful, cost-effective approach to reducing P losses from livestock farms and will help farmers meet increasingly stringent environmental regulations. This paper reviews opportunities available to reduce the P content of livestock manure, including more accurate interpretation of the published P requirements of animals, improved diet formulation and group-feeding strategies to more precisely meet requirements, and approaches to improve availability of feed P for monogastric and ruminant species.

Key Words: Cattle, Phosphorus Excretion, Phytase, Poultry, Swine

© 2004, by the American Society of Animal Science. All rights reserved.

J. Anim. Sci. 2004. 82(E. Suppl.):E173-E195

Implications

Phosphorus-based nutrient management regulations increase the amount of land required to dispose of manure, and will have a detrimental effect on the economy in areas of intensive animal agriculture. Opportunities available now to decrease the P content of livestock manure include more accurate interpretation of published P requirements, more precise diet formulation, and utilization of exogenous phytase or low-phytic acid grains in monogastric diets. Improved grouping strategies to decrease variation within groups of animals, and reduced feed wastage will also reduce the P content of land-applied waste. Together, these strategies may decrease the P content of manure by 40 to 60% in swine and poultry and by 25 to 40% in ruminants. Additional research is needed to better define the P requirements of livestock and the availability of P from feed. Reducing the P content of manure through nutrition is a powerful, cost-effective approach to reducing P losses from livestock farms.