Submitted to: Journal of Dairy Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/15/2005
Publication Date: 5/15/2005
Citation: Misselbrook, T., Powell, J.M., Broderick, G.A., Grabber, J.H. 2005. Dietary manipulation in dairy cattle to reduce ammonia emissions. Journal of Dairy Science. 88:1765-1777. Interpretive Summary: Changing a lactating dairy cow's diet to improve crude protein (CP) use efficiency can alter the quantity and form of nitrogen (N) excreted in manure and impact the emission of ammonia from manure. Reducing dietary CP content lowered both total N excretion in manure and the proportion of the N excreted in urine. Ammonia emissions from fresh slurries applied to a barn floor were unaffected by dietary CP level despite great diet differences in urine urea-N concentrations. This may have been due to lack of urease activity. Cumulative ammonia emissions from fresh slurries applied to soil represented 18% of applied N for both the low and high CP diets. Following storage, cumulative emissions from slurries from a low CP diet were lower (9% of total applied manure N) than slurries from a high CP diet (25% of total applied manure N). Increasing the content of condensed tannins in forage legumes fed in the diet decreased the proportion of N excreted in urine and lowed ammonia emissions from the barn floor and from slurries applied to soil. Manipulating the CP and forage tannin content of dairy diets can alter manure N excretion and ammonia emissions after manure deposition on barn floors or application to soil. These ammonia emission reductions can lead to improvements in air quality.
Technical Abstract: Improvements to the efficiency of dietary nitrogen (N) use by lactating dairy cattle can be made by altering the level and form of protein in the diet. This study collected urine and feces from dairy cows from selected crude protein (CP) treatments of two lactation studies. From the protein level study, collections were made from cattle fed a diet with a high (19.4%) or low (13.6%) CP content (HCP and LCP, respectively). From the protein form trial, collections were made from cattle fed diets in which the forage legume component contained different levels of condensed tannins (CT) being either alfalfa (ALF) or birdsfoot trefoil with a low (BFTL) or high (BFTH) level of CT. A system of small laboratory chambers was used to measure ammonia (NH3) emissions over 48 h from applications of equal quantities of urine and feces to cement (simulating a barn floor) and from applications of slurries, made by combining feces and urine in the proportions in which they were excreted for each treatment, to soil. Reducing dietary CP content resulted less total N excretion and in a smaller proportion of the excreted N being present in urine; urine N concentration was 90% greater for HCP than LCP. Surprisingly, NH3 emissions from the barn floor were similar in absolute terms despite the great differences in urine urea-N concentrations, presumably because urease activity was limiting. Cumulative emissions from fresh slurries applied to soil represented 18% of applied N for both HCP and LCP. Following storage at 20°C for two weeks, cumulative emissions from LCP were much lower than for HCP, representing 9 and 25% of applied N, respectively. Emissions were also lower when expressed as a proportion of slurry total ammoniacal N (TAN) content (24 and 31%, respectively) because of treatment differences in slurry pH. Increasing CT content of the dietary forage legume component resulted in a shift in N excretion from urine to feces. Cumulative NH3 emissions from the barn floor were greater for ALF than either BFTL or BFTH. Emissions from fresh and stored slurries were in proportion to slurry TAN contents, with approximately 35% of applied TAN being lost for all treatments. Emissions expressed as a proportion of total N applied were consistently lower for BFTH than for ALF.