Submitted to: Manure Management Conference Proceedings
Publication Type: Proceedings
Publication Acceptance Date: August 30, 2009
Publication Date: September 29, 2009
Citation: Todd, R.W., Cole, N.A., Parker, D.B., Rhoades, M., Casey, K. 2009. Effect of feeding distiller's grains on dietary crude protein and ammonia emissions from beef cattle feedyards. In: Proceedings of the Texas Animal Manure Management Issues Conference, September 29-30, 2009, Round Rock, Texas. p. 37-44. Interpretive Summary: Feeding wet distiller's grains (WDG), a feed byproduct of ethanol production, can increase the amount of crude protein in beef cattle diets above that needed by animals. Excess nitrogen in diets is excreted and has the potential to increase the nitrogen lost from manure as ammonia. Two years of near-continuous ammonia emission data at two feedyards were used to assess the effect of feeding WDG on ammonia emissions. When diets at the two feedyards were similar, there was no significant difference between them in dietary crude protein or ammonia emisisons. Subsequently, feeding WDG at one feedyard significantly increased dietary crude protein and almost doubled ammonia emissions, compared with the feedyard that did not feed WDG. Feeding WDG utilizes a valuable byproduct, but the increased nitrogen due to WDG results in increased ammonia emissions. The feeding of WDG complicates efforts to reduce ammonia emissions from cattle feedyards.
Technical Abstract: Diversion of corn grain to ethanol production more than doubled from 2003 to 2008. A feed byproduct of ethanol fermentation is distillers grains. Optimum beef cattle diets have crude protein (CP) contents of 12.5%-13.5%, but diets that contain distillers grains in place of corn can have CP that varies from 15% to more than 20%. Most excess N in cattle diets is excreted, so that feeding distillers grains has the potential to increase N lost from manure as ammonia. Twenty-five months of near-continuous ammonia emission data at two feedyards (Feedyards A and E) were used to assess the effect of feeding wet distillers grains (WDG) on ammonia emissions. Three distinct feeding periods were identified: 1) corn-based rations were fed at the two feedyards from February 2007 through December 2007 (Pre-WDG); 2) up to 24% WDG was substituted for corn in rations at Feedyard A (FYA) from February 2008 through October 2008, while Feedyard E (FYE) continued feeding a corn-based ration (FYA-WDG); 3) corn-based rations were fed at both feedyards from December 2008 through February 2009 (Post-WDG). During the Pre-WDG period, CP in rations was not significantly different (P=0.08) between the feedyards (14.4% at FYA and 13.5% at FYE). Ammonia emission, also, was not significantly different (P=0.79, 98 and 95 g NH3-N head**-1 d**-1 at FYA and FYE, respectively). During the FYA-WDG period, both CP (P=0.0006) and per capita ammonia emission rate (P=0.003) were significantly greater at FYA (16.3% CP, 149 g NH3**-N head**-1 d**-1) than at FYE (12.2% CP, 82 g NH3**-N head**-1 d**-1). Crude protein was not significantly different (P=0.20) during the Post-WDG period, though ammonia emission was greater (P=0.01) at FYA, compared with FYE. Feeding WDG utilizes a valuable byproduct increasingly available as corn is diverted to ethanol production, but the increased CP due to WDG results in increased ammonia emissions. The feeding of WDG thus complicates efforts to reduce ammonia emissions from cattle feedyards.