Nutrient Use Efficiency in Animal Agriculture.

Escalating feed and fertilizer prices and increasing regulations to reduce agricultural nutrient loss and environmental contamination have created new and immediate pressures for animal agriculture. Moreover, the recent publication “Livestock’s Long Shadow” has heightened community awareness about negative social and environmental impacts of animal agriculture at regional and global scales. Over the past 20 years or so, much effort has been devoted to recommendations and plans that aim to enhance nutrient use and overall environmental performance of animal agriculture. But what improvements can we realistically expect? Nutrients contained in feed, manure and fertilizer cycle continuously through production system components. Poultry, swine, beef and dairy cattle are fed to produce eggs, meat, milk, and other products; manure and fertilizers are land-applied to grow grain, forage and other products; and so on. High nutrient use in animal production systems can be associated with many factors, including inherent biological inefficiencies with which nutrients are incorporated into livestock, crop and other products, perceived risks of inadequate nutrient use, marketing strategies, and the historic wide-spread availability of nutrients at low cost. Of total feed protein and minerals consumed by poultry, swine, beef and dairy cattle, general averages of only 60, 50, 20 and 30 percent, respectively are actually incorporated into animal products in commercial operations, with the remainder excreted in manure. Field crops have similar nutrient use efficiencies, incorporating a general average range of 30-60 percent of fertilizer and manure nutrients into products. Because of inherent inefficiencies in nutrient use, nutrient loss to the environment is inevitable. We examine gaps between actual outcomes of nutrient use in components of commercial animal production systems and biological potentials as determined in controlled experimental conditions. Assessments of nutrient use potentials are needed to devise realistic nutrient management plans that meet multiple producer and policy objectives.