Effects of roughage source and inclusion in beef finishing diets containing corn wet distillers' grains plus solubles

Two experiments were conducted to determine the effects of roughage source and inclusion in diets containing wet distillers' grains plus solubles (WDGS) on finishing cattle performance and ruminal metabolism. In Exp. 1, 385 crossbred steer calves (initial BW = 346 kg [SD 29]) were used in a finishing trial. A control diet with no roughage inclusion was compared with 6 diets containing either alfalfa hay (ALF), corn silage (CSIL), or corn stalks (CSTK) at 2 inclusions as a 3 x 2 factorial. Alfalfa hay was included at 4 (low) or 8% (standard) of diet DM. Diets containing CSIL or CSTK were formulated to provide total dietary NDF equal to the low and standard ALF inclusion diets. The final diets contained 6.13 and 12.26% CSIL or 3.04 and 6.08% CSTK (DM basis). All diets contained 30% WDGS and a 1: 1 mixture of dry-rolled and high-moisture corn (DM basis). Cattle fed no roughage had reduced (P < 0.01) DMI and tended (P <= 0.10) to have the lowest final BW and ADG compared with cattle fed roughage. There were no differences (P >= 0.11) in DMI, ADG, or G:F due to roughage source. Cattle fed a standard inclusion of roughage had greater (P <= 0.04) DMI and ADG compared with cattle fed diets with low inclusion, regardless of roughage source. Feed efficiency tended to be different among treatments (P = 0.09), with cattle fed no roughage having greater G:F than all treatments (P <= 0.06) except cattle fed the low level of CSTK, which had a similar G: F (P = 0.48). Feed efficiency was not affected by source of roughage (P = 0.23) or inclusion of roughage (P = 0.49). In Exp. 2, 6 ruminally fistulated steers (347 kg BW [SD 25]) were used in a 6 x 6 Latin square design. Treatments were arranged as a 2 x 3 factorial with ALF or CSTK included at zero, low, or standard levels similar to Exp. 1. Apparent total tract digestibility (%) of DM, OM, and NDF decreased linearly (P <= 0.07) due to increasing roughage inclusion. Average, maximum, and minimum ruminal pH increased linearly (P <= 0.09) as roughage inclusion was increased. Based on the results of this study, low levels of CSTK improved cattle performance relative to low inclusions of ALF or CSIL. Diets with standard inclusions of ALF, CSIL, or CSTK had similar performance. Roughage sources can be exchanged to provide equal NDF in finishing diets containing 30% WDGS without negatively impacting finishing cattle. Based on ADG, eliminating roughages when 30% WDGS was included in finishing diets was not beneficial.