Cereal grains in feedlot rations: Influence of type and method of processing upon starch and protein digestibility

摘要

Scope and method of study. Five grains (wheat, oats, corn, barley, and milo), processed by two to five methods (rolling, high moisture ensiling (25% and 35% high moisture), steam flaking, and steam rolling) were fed to five steers in three 5 x 5 latin square experiments to investigate the effect of cereal grain type and method of processing upon the site and extent of digestion. These rations were also fed to three steers in six 3 x 3 latin square experiments to determine the effect of grain type and method of processing upon in situ dry matter and nitrogen disappearance.;Findings and conclusions. Rolled milo had less ruminal and total starch digestion than rolled corn, barley, wheat, or oats. More extensive grain processing tended to lower ruminal pH, lower ruminal ammonia, and increase fecal pH values, but grain particle passage rates and rumen volumes were not altered. As extent of processing increased, total starch digestion increased, primarily due to increased ruminal digestion. Wheat had less (50.5 vs 79.4 and 84.5%) ruminal escape protein and produced greater ruminal ammonia concentrations than corn or milo. Total tract nitrogen digestion was related positively with total tract starch digestion (r =.49; P $<$.0001). Total tract digestion of protein tended to increase but ruminal digestion was decreased by more extensive processing. In situ trials revealed several interactions between the grain fed and grain incubated in the dacron bag on ruminal dry matter disappearance, presumably due to ruminal pH. In situ dry matter disappearance was 1.85% faster (P $<$.05) with 35% high moisture corn than with rolled corn and 1.99% and 2.79% faster with rolled corn and barley than rolled oats. Rates of nitrogen digestion were not affected by the grain type, but protein solubility tended to be decreased by heat processing treatments, presumably due to alteration of the more soluble proteins.