Submitted to: International Conference on Air Pollution from Agricultural Operations
Publication Type: Proceedings
Publication Acceptance Date: 9/12/2003
Publication Date: 10/12/2003
Citation: Cole, N.A., Clark, R.N., Todd, R.W., Richardson, R., Gueye, A., Greene, L.W., Mcbride, K. 2003. Influence of dietary crude protein on potential ammonia emissions from beef cattle manure. International Conference on Air Pollution from Agricultural Operations. p. 183-188.
Interpretive Summary: Atmospheric emissions of ammonia, as well as other gasses and particulates are a growing concern of livestock producers, the general public and regulators. The concentration and form (protein that is rapidly digested in the rumen vs. protein that is slowly degraded in the rumen) of protein in beef cattle diets can affect urinary and fecal excretion of nitrogen and thus may affect ammonia emissions from beef cattle feedyards. To determine the effects of dietary protein concentration and degradability on potential ammonia emissions we measured the quantity of ammonia produced from the feces and urine of steers fed 9 different diets. The diets differed in protein concentration (11.5, 13 and 14.5%) and degradability (rapid, moderate, slow) of the supplemental protein. Feces and urine excreted were collected added to polyethylene chambers containing 1,550 g of soil. Chambers were sealed and ammonia emissions were trapped in an acid solution using a vacuum system. Results suggested that as the protein concentration in the diet increases from 11.5 to 13%, potential daily ammonia emissions increased 60% or more, due primarily to increased urinary N excretion. As days on feed increased, ammonia emissions also increased. Although daily ammonia emissions may be affected by diet, these emissions must be balanced with possible effects on animal performance to determine optimal protein concentrations and forms of feedlot cattle.
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.