INTERACTION OF FEED-INTAKE LEVEL ON COMPARATIVE RUMINAL AND TOTAL TRACT DIGESTION OF DRY-ROLLED AND STEAM-FLAKED CORN

Four Holstein steers (208 kg) with ''T'' cannulas in the rumen and pro ximal duodenum were used in a 4 x 4 Latin square design experiment to evaluate the interaction of feed intake level on comparative ruminal a nd total tract digestion of dry-rolled and steam-flaked corn. The basa l diet contained (DM basis) 6% alfalfa hay, 6% sudangrass hay, 75% cor n, 2% yellow grease; 5% cottonseed meal, 3% cane molasses, and 3% supp lement. The corn portion of the diet was provided as either dry-rolled (density =.54 kg/L) or steam-flaked (density =.36 kg/L). Dry matter i ntake was restricted to allow for .64 vs 1.28 kg/d of weight gain (1.6 vs 2.4% of BW). Ruminal digestibility of OM, starch, and feed N were not affected (P >.10) by DMI. Postruminal digestion of OM and N and to tal tract digestibility of OM and DE decreased (P <.05) as DMI was inc reased. Total tract starch digestibility was not influenced (P >.10) b y DMI. Steam flaking corn increased (P <.05) ruminal digestibility of OM and starch and postruminal and total tract digestibility of OM, sta rch, N, DE, and ME. Increasing DMI and steam flaking decreased (P <.05 ) ruminal pH and molar proportion of acetate. It is concluded that cor n processing is the primary factor influencing site and extent of star ch digestion. Decreasing DMI increases DE value of,the diet; however, ME value is not affected because of increased energy loss as methane.