Recent advances to improve nitrogen efficiency of grain-finishing cattle in North American and Australian feedlots

Authors: COWLEY, FRAN - University Of New England; JENNINGS, JENNY - Texas A&M Agrilife; COLE, N. ANDY - Retired ARS Employee; BEAUCHEMIN, KAREN - Aafc Lethrdge Research Center

Submitted to: Animal Production Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/7/2019
Publication Date: 9/16/2019
Citation: Cowley, F., Jennings, J., Cole, N., Beauchemin, K. 2019. Recent advances to improve nitrogen efficiency of grain-finishing cattle in North American and Australian feedlots. Animal Production Science. https://doi.org/10.1071/an19259.
DOI: https://doi.org/10.1071/an19259

Interpretive Summary: There is increasing need to improve the utilization of protein and the nitrogen (N) within the protein by feedlot cattle – from both an economic and environmental standpoint. In general feedlot cattle retain 10 to 20% of the protein (i.e. N) they are fed. The rest is excreted in feces and urine. The excreted N leaves the feedlot either as manure (which is normally used to fertilize crops), as gases such as ammonia, or as runoff into retention ponds or lagoons. Thus, there is a need to increase the percentage of N retained by the animal in order to decrease N excretion and to decrease gaseous losses from the feedlot. Scientists from ARS (Bushland, TX), Texas A&M AgriLife Research, University of New England (Australia) and AgriFoods Canada reviewed of the literature concerning feedlot N use efficiency written from the perspective of beef cattle nutritional scientists in Australia, Canada, and the United States. The review covers the topics: 1) the need for improved N efficiency; 2) gaseous emissions from feedyards and mitigation strategies; 3) animal protein requirements and the supply in feed ingredients; 4) metabolism of protein and N within the gut and tissues of the animal; 5) the energetic costs of overfeeding protein; 6) benefits of feeding high protein diets; and 7) strategies to optimize N use efficiency (oscillating dietary protein concentrations, phase feeding of protein, interactions with growth promoters, etc.). These findings will be of interest to other animal scientists and feedlot operators.

Technical Abstract: There is increasing need to improve the utilization of protein and the nitrogen (N) within the protein by feedlot cattle – from both an economic and environmental standpoint. In general feedlot cattle retain 10 to 20% of the protein (i.e. N) they are fed. The rest is excreted in feces and urine. The excreted N leaves the feedlot either as manure (which is normally used to fertilize crops), as gases such as ammonia, or as runoff into retention ponds or lagoons. Thus, there is a need to increase the percentage of N retained by the animal in order to decrease N excretion and to decrease gaseous losses from the feedlot. Scientists from ARS (Bushland, TX), Texas A&M AgriLife Research, University of New England (Australia) and AgriFoods Canada reviewed of the literature concerning feedlot N use efficiency written from the perspective of beef cattle nutritional scientists in Australia, Canada, and the United States. The review covers the topics: 1) the need for improved N efficiency; 2) gaseous emissions from feedyards and mitigation strategies; 3) animal protein requirements and the supply in feed ingredients; 4) metabolism of protein and N within the gut and tissues of the animal; 5) the energetic costs of overfeeding protein; 6) benefits of feeding high protein diets; and 7) strategies to optimize N use efficiency (oscillating dietary protein concentrations, phase feeding of protein, interactions with growth promoters, etc.). These findings will be of interest to other animal scientists and feedlot operators.