Submitted to: Journal of Animal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/29/2004
Publication Date: 2/1/2005
Citation: Cole, N.A., Clark, R.N., Todd, R.W., Richardson, C.R., Gueye, A., Greene, L.W., McBride, K. 2005. Influence of dietary crude protein concentration and source on potential ammonia emissions from beef cattle manure. Journal of Animal Science. 83:722-731.
Interpretive Summary: Atmospheric emissions of ammonia, as well as other gases and particulates are a growing concern of cattle producers, the general public and regulators. The concentration and digestibility of protein in beef cattle diets may affect the amount and form of nitrogen that is excreted 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 fed steers nine different diets that contained three protein concentrations and three supplemental protein sources. Feces and urine collected from the steers were used to measure lab-scale ammonia losses. As the protein concentration in the diet increased from 11.5 to 13% ammonia losses increased but losses were similar on the 13 and 14.5% protein diets. Ammonia losses increased as the days on feed increased. The major factors controlling ammonia losses were urinary N and urinary urea-N excretion. These results demonstrate that dietary protein can affect ammonia emissions from beef cattle feedyards. They also demonstrate that the use of phase feeding (i.e. decreasing dietary protein concentration as days on feed increases to better match dietary protein with requirements) can potentially have a major effect on ammonia emissions. However, decreasing dietary protein concentrations can potentially affect animal health and performance. Therefore, potential daily ammonia emissions must be balanced with possible effects on animal performance and animal health to determine optimal protein concentrations and forms for feedlot diets.
Technical Abstract: Atmospheric emissions of ammonia, as well as other gases and particulates are a growing concern of livestock producers, the general public and regulators. The concentration and ruminal degradability of protein 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 protein concentration and degradability on potential ammonia emissions, 54 steers were randomly assigned to 9 dietary treatments in a 3 x 3 factorial arrangement of treatments. Treatments consisted of three dietary CP concentrations (11.5, 13, and 14.5%) and three supplemental urea:cottonseed meal ratios (100:0, 50:50, and 0:100 of supplemental N). Steers were confined to tie stalls and feces and urine excreted were collected and frozen on approximately days 30, 75, and 120 on feed. One percent of daily urine and feces excretion were mixed and added to polyethylene chambers containing 1,550 g of soil. Chambers were sealed and ammonia emissions were trapped in an acid solution for seven days using a vacuum system. As the protein concentration in the diet increased from 11.5 to 13%, in vitro daily ammonia emissions increased (P < 0.01) 60 to 200 %, due primarily to increased urinary N excretion. As days on feed increased, in vitro ammonia emissions also increased (P < 0.01). Potential ammonia losses were highly correlated to urinary N (r2 = 0.69) and urinary urea-N (r2 = 0.58) excretion. Urinary nitrogen excretion was correlated to plasma urea N concentration (r2 = 0.52) and intake of degradable protein (r2 = 0.23). Although dietary composition can affect daily ammonia losses, daily ammonia emissions must be balanced with effects on animal performance to determine optimal protein concentrations and forms in the diet.