Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: 4/22/2003
Publication Date: 6/22/2003
Citation: Cole, N. A., Clark, R. N., Todd, R. W., Richardson, C. R., Gueye, A., Greene, L. W., Mcbride, K. Influence of Dietary Crude Protein on Potential Ammonia Emissions From Beef Cattle Manure. Journal of Animal Science. 2003. v. 81(Suppl.1). p. 110. Abstract No. 436.
Technical Abstract: Atmospheric emissions of ammonia is a growing concern of livestock producers, the general public, and regulators. The concentration and form (rapidly degradable vs. undegradable in the rumen) of CP in beef cattle diets may affect urinary and fecal excretion of nitrogen and thus may affect ammonia emissions from beef cattle feedyards. To determine the effects of dietary CP concentration and degradability on potential ammonia emissions, 54 steers were randomly assigned to 9 dietary treatments in a 3 x 3 factorial arrangement. Treatments consisted of three dietary CP concentrations (11.5, 13, and 14.5 percent, DM basis) and three supplemental urea: cottonseed meal ratios (100:0, 50:50, and 0:100 of supplemental N). On three occasions during the feeding period (approximately 35, 75 and 115 days) steers were confined to tie stalls and feces and urine excreted were collected for five days and frozen. One percent of thawed daily urine and feces excretion were mixed and added to polyethylene chambers containing 1,550 g of soil. Chambers were sealed and ambient air was drawn through the chambers at a rate of 1.5 L/min using a vacuum pump. Ammonia in the outgoing air was trapped in a 0.9 molar sulfuric acid solution for seven days. Ammonia emissions were highly correlated to urinary N excretion and application [ammonia emissions = 0.723(urine N) - 10.29: r = 0.78; P < 0.01; ammonia emissions and urine N in mg]. As the CP concentration in the diet increased from 11.5 to 13 percent potential daily ammonia emissions increased 60 to 225 percent (d 30 and 115, respectively). Ammonia losses for steers fed the 13 and 14.5 percent CP diets were not significantly different, probably because urinary N excretions were not different. As days on feed increased, in vitro ammonia emissions also increased due to increased urinary N excretion (P < 0.01). On days 75 and 115 urinary N excretion and ammonia emissions increased (P < 0.10) as the proportion of urea in the supplement increased. This study indicates that dietary CP concentration and degradability may affect daily emissions of ammonia from beef cattle feedlots. However, daily ammonia emissions must be balanced with possible effects on animal performance to determine optimal CP concentrations and forms in finishing diets.