Supplemental cracked corn for steers fed fresh alfalfa: I. Effects on digestion of organic matter, fiber, and starch.

The effect of supplementation with different levels of cracked corn on the sites of OM, total dietary fiber (TDF), ADF, and starch digestion in steers fed fresh alfalfa indoors was determined. Six Angus steers (338 +/- 19 kg) fitted with cannulas in the rumen, duodenum, and ileum consumed 1) alfalfa (20.4% CP, 41.6% NDF) ad libitum (AALF); 2), 3), and 4) AALF supplemented (S) with .4, .8, or 1.2%, respectively, of BW of corn; or 5) alfalfa restricted at the average level of forage intake of S steers (RALF), in a 5 x 5 Latin square design. Total OM intake was lower (P < .01) in steers fed RALF than in those fed AALF but level of forage intake did not affect sites of OM, TDF, or starch digestion (P > .05). Forage OM intake decreased (P < .01) linearly (8,496 to 5,840 g/d) but total OM intake increased (P = .03) linearly (8,496 to 9,344 g/d) as corn increased from .4 to 1.2% BW. Ruminal apparent and true OM disappearance was not affected, but OM disappearing in the small intestine increased (P < .01) linearly with increasing levels of corn. Total tract OM digestibility (71.2 to 76.2%) and the proportion of OM intake that was digested in the small intestine (15.4 to 24.5%) increased (P < .01) linearly as corn increased. The TDF and ADF intakes decreased (P < .01) linearly as level of corn increased. Total tract TDF and ADF digestibilities were not different among treatments (average 62.9 and 57.8%, respectively). Starch intake and starch digested in the rumen and small and large intestine increased (P < .01) linearly with increasing corn level. Ruminal pH and VFA concentrations decreased and increased (P < .01), respectively, with increasing corn. Supplementation with corn increased OM intake, decreased forage OM intake, and increased the proportion of OM that was digested in the small intestine, but fiber digestion was not affected.