REDUCING CRUDE PROTEIN IN BEEF CATTLE DIET REDUCES AMMONIA EMISSIONS FROM ARTIFICIAL FEEDYARD SURFACES

Authors: Todd, Richard; Cole, Noel; Clark, Ray

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/28/2005
Publication Date: 2/2/2006
Citation: Todd, R.W., Cole, N.A., Clark, R.N. 2006. Reducing crude protein in beef cattle diet reduces ammonia emissions from artificial feedyard surfaces. Journal of Environmental Quality. 35:404-411.

Interpretive Summary: Ammonia, when a source of excess nitrogen, can be a serious environmental pollutant, especially in nutrient-sensitive ecosystems like forests, prairies, lakes or estuaries. Concentrated animal feeding operations are major sources of ammonia to the atmosphere. Effective control methods exist to reduce emissions, but many are impractical or uneconomical. For beef cattle, decreasing crude protein in diets may be the most workable way to reduce ammonia emissions. Previous research showed that weight gain did not suffer when cattle were fed a diet with 11.5% crude protein, instead of the more common 13% crude protein diet. We wanted to see if decreasing crude protein in the diet could also decrease ammonia emission. Two groups of steers were fed a diet with either 11.5% or 13% crude protein and all manure was collected. The manure was applied to circular plots during four seasons and ammonia emission measured. Decreasing crude protein in beef cattle diets from 13% to 11.5% significantly decreased mean daily ammonia emission by 30%, 52% and 29% in summer, autumn and spring field trials, respectively. No significant difference was observed in winter. On an annual basis, decreasing crude protein reduced daily ammonia emission by 28%. The magnitude of reduction would depend on many factors, such as the ability to precisely formulate and feed rations, genetic variation in cattle, environmental variability, and manure management. In spite of these uncertainties, reducing crude protein in beef cattle diets may provide the most practical and economical way to reduce ammonia emissions from feedyards.

Technical Abstract: Concentrated animal feeding operations are major sources of ammonia to the atmosphere. Control methods to reduce emissions include acidifying amendments, urease inhibitors, and absorbents. For beef cattle, decreasing crude protein in diets may be the most practical and cost-effective method to reduce ammonia emissions. The objective of this research was to quantify the effect of reducing crude protein (CP) in beef cattle diet on ammonia emissions. Two groups of steers were fed a diet with either 11.5% or 13.0% CP and all urine and feces were collected. Manures from the two diets were applied in a replicated laboratory closed chamber experiment, and ammonia emission was quantified using acid gas washing. In four seasonal field trials, manures from the two diets were applied to two 5-m diameter, circular, artificial feedyard surfaces, and ammonia emission was quantified using the micrometeorological integrated horizontal flux method. Decreasing crude protein in beef cattle diets from 13% to 11.5% significantly decreased ammonia emission by 44% in the closed chamber laboratory experiment, and significantly decreased mean daily ammonia flux by 30%, 52% and 29% in summer, autumn and spring field trials, respectively. No significant difference was observed in winter. On an annual basis, decreasing crude protein reduced daily ammonia flux by 28%. From 79% to 99% of applied manure N was emitted as NH3-N during the summer trial; during other seasons, less than half of the applied N was emitted. Reducing crude protein in beef cattle diets may provide the most practical and cost-effective way to reduce ammonia emissions from feedyards, in spite of challenges in feed and manure management, and variability in animal genetics and feeedyard environment.