Submitted to: Texas A&M Research and Extension Center Progress Report
Publication Type: Experiment Station
Publication Acceptance Date: 7/2/2003
Publication Date: 8/1/2003
Citation: Dew, P., Brown, M.S., Cole, N.A., Drager, C.D. 2003. Effect of degreee of corn processing on site and extent of digestion by beef steers. Texas A&M Research and Extension Center Progress Report. p. 44-49.
Interpretive Summary: Feed grains fed to finishing beef cattle are normally processed in some manner before being fed. This is to increase grain digestibility, decrease manure production, and improve animal performance. Starch and proteins in cattle feeds can be digested in the forestomach (rumen and reticulum) or in the intestine. The site of digestion can have a profound effect on how efficiently the feed is utilized. Therefore this study was conducted to determine the effects of corn processing on site and extent of digestion. Corn was processed by dry rolling or steam flaking to a bulk density of 0.36 or 0.28 kg/L (28 and 22 pounds/bushel, respectively) before inclusion into 90% concentrate diets fed. Enzymatically available starch averaged 25, 60, and 74% of total starch for dry rolled, steam flaked to 28 lb/bu, and steam flaked to 22 lb/bu, respectively. The pH of ruminal fluid was not influenced by the degree of processing. Ruminal, intestinal, and total tract starch digestibility were greater for steam flaked corn than dry rolled corn. Ruminal digestibility of feed N and synthesis of microbial protein by ruminal bacteria (g of microbial nitrogen/kg of organic matter fermented) was lower for steam flaked corn diets than the dry rolled corn diet. Total tract nitrogen and phosphorus digestibility were not affected by degree of corn processing. Increasing the degree of corn processing increased the extent of ruminal and total tract organic matter and starch digestion, and decreased the extent of ruminal feed nitrogen digestion and microbial efficiency. These differences could influence the animal's protein requirements.
Technical Abstract: Five crossbred beef steers (average BW 336 kg) with cannulas in the rumen and duodenum were used in a 5 x 3 Incomplete Latin square to evaluate the effect of degree of corn processing on site and extent of diet digestion. Corn was processed by dry rolling (DRC) or steam flaking (SF) to a bulk density of 0.36 or 0.28 kg/L (28 [SF28] and 22 [SF22] pounds/bushel, respectively) before inclusion into 90% concentrate diets fed every 2 h. Enzymatically available starch, expressed as a percentage of total starch for DRC, SF28, and SF22, averaged 25, 60, and 74%. Ruminal fluid pH was not influenced (P = 0.15) by the degree of processing (5.89, 5.63, and 5.62 +/- 0.15); however, duodenal pH responded quadratically (P = 0.03; 2.58, 2.22, and 2.51 +/- 0.17). Ruminal and total tract starch digestibility increased quadratically (P < 0.08); ruminal and total tract starch digestibility were greater (15 and 5%, respectively) for SF28 and SF22 than DRC. Site and extent of OM digestion closely resembled changes in starch digestion. Postruminal starch digestibility (% of entry) was 49% greater (P = 0.01) for SF28 and SF22 than DRC. Ruminal feed N digestibility and microbial efficiency (g of microbial N/kg of OM truly fermented) was lower (P < 0.08) for SF28 and SF22 than DRC. Total tract N digestibility, and ruminal and postruminal P digestibility were not influenced (P > 0.24) by degree of corn processing. Degree of processing did not consistently affect total tract P digestion (quadratic effect, P = 0.09). Total tract ADF digestibility decreased linearly with an increasing degree of processing (P = 0.02), whereas total tract NDF digestibility decreased quadratically (P = 0.07). Increasing the degree of corn processing increased the extent of ruminal and total tract organic matter and starch digestion, and decreased the extent of ruminal feed nitrogen digestion and microbial efficiency.