Influence of energy source on forage intake, digestibility, in situ forage degradation, and ruminal fermentation in beef steers fed medium-quality brome hay

Eight ruminally cannulated steers (average initial weight 196 +/- 13 kg) were arranged in a replicated 4 X 4 Latin square. Steers had ad libitum access to chopped brome hay (Bromus inermus L. 9.9% CP) and one of four supplements. Supplements were fed to provide 195 g of CP.steer-1.d-1 (equalized with soybean meal), and supplemental energy intake was similar among energy supplements. Supplemental treatments were control (CTRL; primarily soybean meal), barley (BAR), beet pulp (PULP), and corn (CORN). Amounts fed were 481, 1,285, 1,335, and 1,289 g of DM.steer-1.d-1 for CTRL, BAR, PULP, and CORN, respectively. Individually stanchioned steers were allowed a 13-d adaptation period followed by an 8-d collection period. Chromic oxide was used as the indigestible flow marker. Forage intake was less (P < .10) for steers fed BAR, PULP, and CORN than for CTRL steers, but total intake (forage + supplement) did not differ among treatments. Total tract DM and OM digestibilities were greater (P < .10) for PULP- and CORN- than for CTRL- and BAR-supplemented steers. Digestibility of NDF was least (P < .10) for BAR, intermediate for CORN, and greatest for CTRL and PULP (44.0, 47.2, 50.1, and 52.1%, respectively). Apparent CP digestibility was least (P < .10) in BAR- (60.8), greatest in CTRL- (69.7), and intermediate in PULP- and CTRL- (64.0 and 64.4) supplemented steers. Ruminal DM fill was less (P < .10) in steers fed BAR and PULP than in CTRL steers. No differences (P < .10) were noted in DM and NDF rate of in situ degradation. Rate of forage CP in situ degradation was faster (P < .10) in CTRL- and PULP- than in CORN- and BAR-supplemented steers. Steers fed BAR and PULP supplements exhibited a lower overall pH response curve (P < .005) than did steers fed CTRL and CORN; this finding corresponded to increased (P < .005) response curves in PULP-fed steers for total VFA, acetate, and propionate compared with other treatments. These data indicate that energy supplementation decreased forage intake, altered ruminal fill, shifted VFA patterns, and changed in situ rate of forage CP degradation. Moreover, PULP maintained NDF digestibilities equal to CTRL levels, whereas CORN and BAR did not.