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Environmental stewardship in the future: Nutrient management issues and options for beef cattle feeding operations

Department of Animal Science and Food Technology, Texas Tech University, Lubbock 79409-2141

Abstract

Confinement feeding of beef cattle concentrates nutrient wastes, which could lead to environmental concerns. At present, public and legislative concern seems to be focused on excretion of N and P. Nutrient input should be a function of the animal's requirement for a given nutrient, with diets then formulated to meet the requirement given an expected or predicted feed intake. With N, however, estimates of animal requirements vary greatly between the two main systems used for calculation of requirements. Nitrogen requirements calculated with the factorial system are considerably lower than those calculated with the metabolizable protein system. Current industry formulation practices and some recent research data agree more closely with requirements calculated by the metabolizable protein system. Nitrogen and P excretion could be decreased by applying a phase-feeding approach in which diet formulas are changed with time on feed to reflect decreasing requirements for these nutrients. In addition, applying restricted or programmed feeding approaches that simply decrease feed intake to some percentage of ad libitum or fix intake to yield a specific rate of gain should decrease nutrient input and ultimately decrease nutrient output. When high-grain diets are fed to finishing beef cattle, limited data suggest little benefit from providing supplemental P. If further research supports these limited data, removal of supplemental P from high-grain beef cattle finishing diets might be an important environmental management option. Accurate estimates of nutrient requirements are vital to both animal well-being and nutrient management issues, and regular revisions of standards set by the National Research Council should be supported by the beef cattle feeding industry.