THE FEEDING VALUE OF DRY-ROLLED AND STEAM-FLAKED CORN IN FINISHING DIETS FOR FEEDLOT CATTLE - INFLUENCE OF PROTEIN SUPPLEMENTATION

We used 80 medium-framed yearling crossbred heifers (357 kg) in a 110- d trial to evaluate the influence of dietary protein level (11 vs 14%) on the feeding value of dry-rolled (DRC) and steam-flaked corn (SFC). All diets contained 1% urea; cottonseed meal (CSM) was the source of supplemental undegradable intake protein (UIP). Steam flaking corn red uced DMI (9%, P < .10) and increased(P < .01) feed efficiency (14%), d ietary NEm (13%), and NEg (15%). Steam flaking increased the NEm by 17 % and NEg by 19%. Supplemental CSM decreased (P < .10) feed efficiency (7%) and dietary NEm (4%) and NEg (6%). There were no treatment effec ts (P > .10) on carcass characteristics. Steam flaking corn increased( P < .05) fecal pH and reduced (P < .01) fecal starch. Supplemental CSM increased (P < .01) fecal pH and reduced(P < .01) fecal starch. Four Holstein steers (413 kg) were used in a 4 x 4 Latin square experiment to evaluate treatment effects on digestive function. Steam flaking cor n increased (P < .05) flow of nonammonia N (11%, P < .05) and microbia l N (15%, P < .01) to the duodenum. Supplemental CSM increased the flo w of microbial N (6%, P < .01), feed N (21%, P < .10), and nonammonia N (12%, P < .05) to the duodenum. The UIP value of CSM was 28% for the DRC diet and 52% for the SFC diet. Steam flaking corn increased (P < .01) ruminal starch digestion (26%) and total tract digestibility of O M (17%), N (15%), starch (19%), and GE (17%). Steam flaking increased the DE value of corn by 21%. Supplemental CSM did not influence (P > . 10) postruminal or total tract starch digestion. Supplemental CSM decr eased (7%, P < .10) the DE value of the diet. We conclude that increas ing the postruminal protein supply of a corn-based finishing diet beyo nd that provided by urea supplementation, alone, will not enhance star ch digestion or the energy value of the diet.