Nitrogen sustainability and beef cattle feedyards: introduction and influence of pen surface conditions and diet

Authors: Waldrip, Heidi; Cole, Noel; Todd, Richard

Submitted to: Trade Journal Publication
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/27/2015
Publication Date: 4/1/2015
Citation: Waldrip, H., Cole, N.A., Todd, R.W. 2015. Nitrogen sustainability and beef cattle feedyards: introduction and influence of pen surface conditions and diet. The Professional Animal Scientist 2015. 31:89-100 doi:10.15232/pas.2014-01361

Interpretive Summary: In the United States, it is important that beef be produced in a way that is economically profitable while minimizing the negative effects on society and the environment. The manure (a mixture of urine and feces) from beef cattle contains high concentrations of nitrogen, which must be managed carefully. Manure nitrogen can be lost to air as ammonia and nitrous oxide, or to water as nitrate and other compounds. Nitrogen loss also means that the manure has lower value as crop fertilizer. Sustainable beef production requires consideration of the long-term effects of management practices. It is also important to have a good understanding of how different environmental and management factors affect the fate of feedyard nitrogen. Nitrogen enters a feedyard in the form of feed and purchased animals. This nitrogen input must be balanced with output from the feedyard as manure and beef. Efforts to improve feedyard sustainability usually involve managing nitrogen balance components for efficiency and low nitrogen losses. A scientific literature review was conducted to evaluate the potential impact of beef cattle feedyards on air, soil, and water quality. This work resulted in a comprehensive analysis of the state-of-the-science regarding feedyard nitrogen. Methods to reduce feedyard nitrogen losses were evaluated. We also identified knowledge gaps and areas where more study is needed. Two key factors were feedyard manure management and cattle diet. Nitrogen balance studies showed that only about 15% of the nitrogen input from cattle feed remained in animal tissue. About 44% of nitrogen output was lost to air or water and 41% of output was nitrogen in manure removed from the feedyard. The concentration and digestibility of protein in cattle feed generally controlled how much nitrogen that cattle eliminated in urine and feces. Most feedyard nitrogen was lost from urine as ammonia gas. Feeding both too much protein and easily digestible protein to cattle increased the amount of nitrogen excreted in urine and losses of ammonia gas. The best way to improve the feedyard nitrogen balance is probably to feed cattle to meet, but not exceed, their protein need for growth. Removing manure from pens more often and treating manure with compounds to lower ammonia and nitrous oxide production might also improve feedyard nitrogen sustainability. More study is needed to improve understanding on the effects of diet and manure management on the fate of feedyard nitrogen.

Technical Abstract: Greater public awareness of the potential effects of agriculture on the environment calls for beef production systems that are sustainable with regard to the environment, society, and the economy. Reactive nitrogen (N) from feedyards could negatively influence air and water quality in the event of volatilization of ammonia and nitrous oxide, and leaching and runoff of nitrate or other forms of organic and inorganic N. Sustainable N management challenges producers to better understand the dynamics of feedyard N and consider the long-term implications of management practices. The concept of N balance is key when considering the role of N in feedyards. Efforts to improve the sustainability of feedyard operations revolve around managing the components of the N balance so that N is used efficiently and losses are minimized. The objectives of this review were to examine the critical components of the feedyard N balance, provide a comprehensive analysis of the state of the science of each component, and identify ways to minimize the negative impacts of N that detract from sustainability. In this work, we reviewed the current literature to assess the impact of beef cattle feedyards on the environment, evaluated methods to mitigate losses of N from feedyards, and identified knowledge gaps and areas requiring further research.Two key factors addressed were feedyard manure management and cattle diet. Nitrogen balance studies showed that only about 15% of the N flow through a feedyard remains in animal tissue (daily average of 25 g per head). Most N (44%) was lost to the atmosphere or as runoff, whereas only 41% was removed with harvested manure. Dietary concentration and ruminal degradability of dietary protein were the primary factors affecting the quantity and route of excretion (urine vs. feces) of N by beef cattle, where excretion of urinary N increased with N intake and with increased dietary ruminally digestible protein. Further study is warranted to improve understanding regarding the effects of diet composition on N transformations and fate on feedyards.