Sites of Organic Matter, Fiber, and Starch Digestion in Steers Fed Fresh Alfalfa and Supplemented with Increased Levels of Cracked Corn

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