REVIEW: Feeding Nitrogen and Phosphorus in Beef Cattle Feedlot Production to Mitigate Environmental Impacts
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2007 American Registry of Professional Animal Scientists. As a result of favorable climatic conditions, availability of feed grains, and location of beef processing facilities, the feedlot cattle industry has become increasingly concentrated in the southern and central Great Plains of the United States. These operations concentrate nutrients in a relatively small area, resulting in environmental issues associated with feedlot cattle such as nutrient pollution of ground and surface water as well as pollution of air. Excreted N and P can cause significant water pollution if directly discharged into surface water through runoff or deposited in water from aerial emissions. In addition, volatilized N in the form of NH3 from voided urine and feces returns to the land or water via rainfall, dry precipitation, or direct absorption. The development of feeding strategies to improve the uti-lization of N by the animal, decreasing N lost to the environment, and improving N-to-P ratio in pen surface manure are likely to mitigate environmental impacts of feedlot cattle. Nutrient requirements of feedlot cattle change during the feeding period. Nonetheless, feedlot cattle are typically fed a constant level of CP and other nutrients from about d 24 of feeding through slaughter. Consequently, CP is often underfed early and overfed late in the feeding period. Feeding nutrients at concentrations that closely match animal requirements can prevent excess excretion of nutrients. The objectives of this review are to discuss the known environmental impacts of beef cattle feedlots and to summarize current feeding strategies to decrease these environmental impacts while maintaining animal performance.