Effect of Roughage Source in Whole Shelled Corn Diets on Feedlot Performance and Digesta Kinetics of Cattle

Two trials (feedlot and metabolism) were conducted to evaluate the effects of roughage source in whole shelled corn (WSC)-based diets fed to beef steers. In the feedlot trial, 296 mixed-breed steers (avg. BW 317 kg) were fed diets consisting of either 6% alfalfa hay (AH), wheat straw (WS), or ammoniated wheat straw (AWS) and 8% corn silage (CS) of diet DM as the roughage source; the remaining portions were WSC and a pelleted protein supplement. Roughage source had little effect (P>0.30) on ADG and feed efficiency over the 134-d feeding period. Feed consumption, however, was lower (P<0.05) for steers fed the WS diet than for the other three diets. Four ruminally and duodenally cannulated beef steers (avg. BW 469 kg) were used in a 4 × 4 Latin square metabolism trial. Ruminal pH was similar for steers fed the CS, WS, and AWS diets, but was higher (P<0.10) for steers fed the AH diet. Total VFA concentration was highly correlated with ruminal (pHR=−0.87) and was lower (P<0.05) in steers fed the AH diet than in those fed the other three diets. Ruminal and total tract digestion of OM, starch, and N, estimated using chromic oxide as a marker, were not affected by roughage source. Results suggest that WS and AWS can replace AH or CS as a roughage source in WSC finishing diets without adversely affecting feedlot performance and (or) site, extent and kinetics of whole corn digestion.