Soybean hull and enzyme inclusion effects on diet digestibility and growth performance in beef steers consuming...

A beef feedlot study was conducted to determine the effects of increasing soybean hull (SH) inclusion and enzyme addition on diet digestibility and animal performance. The hypothesis was SH inclusion and enzyme addition would increase fiber digestibility with no negative effect on animal performance. Eight treatments (TRT) were arranged in a 4 × 2 factorial using four diets and two enzyme (ENZ) inclusion rates. The diets were composed primarily of whole shell corn (WSC) with 0%, 7%, 14%, or 28% SH replacing corn. The ENZ was a commercial proprietary mix of , and (Cattlemace, R&D Life Sciences, Menomonie, WI) included in the diets at 0% (S0, S7, S14, S28) or 0.045% DM basis (S0e, S7e, S14e, S28e). Eighty steers (287 ± 31 kg, SD) were stratified by weight and blocked into pens with 1 heavy and 1 light pen per TRT (2 pen/TRT, 5 steers/pen). Steers were fed for 70 d with titanium dioxide included in the diets for the final 15 d. Fecal samples were collected on d 70 to determine diet digestibility. Diets were balanced for AA and RDP requirement based on available ME. Individual DMI was measured using a GrowSafe system. Diet, ENZ, and diet × ENZ effects were analyzed using the MIXED procedure of SAS. Initial BW was applied as a covariate for final BW (FBW), and DMI was included as a covariate for all digestibility measures. The diet × ENZ interaction had no effect on FBW, ADG, DMI, or any digestibility measure ( ≥ 0.11). Steers fed ENZ tended to have greater FBW ( = 0.09) and had numerically greater ADG than steers not fed ENZ. Diet influenced DMI ( < 0.01), as steers fed S7 diets had the greatest DMI ( ≤ 0.3), steers fed S0 diets had the least DMI ( ≤ 0.002), and DMI of steers fed S14 and S28 diets did not differ ( = 0.5). There was a diet × ENZ interaction for G:F ( = 0.02) in which S0, S0e, S14e, and S28e did not differ ( ≥ 0.3) and were greatest ( ≤ 0.05). There was no effect of diet or ENZ on DM, OM, or CP digestibility ( ≥ 0.2). Diet had an effect on NDF and ADF digestibility ( ≤ 0.04) which decreased as SH inclusion increased. The addition of ENZ tended to decrease NDF digestibility ( = 0.08) but had no effect on ADF digestibility ( = 0.8). Fiber digestibility in WSC diets did not improve with SH inclusion or ENZ addition but steers fed diets with 14% to 28% of WSC replaced by SH and the addition of 0.045% ENZ converted feed at the same rate as steers fed WSC diets with no SH.