Using a fibrolytic enzyme to barley-based finishing diets containing wheat dried distillers grains with soubles: ruminal fermentation, digestibility, and growth performance in feedlot steers
Two experiments were conducted to evaluate the effects of adding an exogenous fibrolytic enzyme (FE) on ruminal pH and fermentation, digestibility, and growth performance in feedlot beef cattle fed finishing diet containing wheat dried distillers grains with solubles (DDGS). In Exp. 1, four ruminally cannulated Angus heifers (averaged BW of 807 ± 93.9 kg) were used in a repeated 4 × 4 Latin square design. Treatments were: 1) control (CON; 10% barley silage and 90% barley grain-based concentrate); 2) WDG (CON diet substituting 30% wheat DDGS for barley grain); 3) WDGL (WDG diet supplementing with low FE; 1 mL FE/kg diet DM); and 4) WDGH (WDG diet supplementing with high FE; 2 mL FE/kg diet DM). Heifers were fed at restriction of 90% ad libitum twice daily. Digestibility in the total digestive tract was measured using Yb as external digesta marker. Statistical contrasts were generated to compare CON vs. WDG and the linear and quadratic effects of FE dosages (0, 1 and 2 mL FE/kg diet). Digestibility of DM was less (P = 0.01) with WDG (67%) than CON diet (71%). Increasing FE linearly (P < 0.05) increased starch digestibility from 88.7, 89.7 to 91.3% without affecting digestibility of other nutrients. Adding FE also reduced (P = 0.03) ruminal ammonia-N concentration from 13.6 to 10.1 mM. In Exp. 2, one hundred and sixty yearling steers (initial BW of 495 ± 37.9 kg) were fed 1 of 4 diets used in Exp. 1. Dry matter intake (10.9 kg/d), final BW (684 kg), and ADG (1.69 kg) did not differ between steers fed CON and WDG diets. However, steers fed WDG reduced (P < 0.05) G:F (150 vs. 160 g/kg DMI) and increased (P < 0.01) percentage of abscessed livers (49 vs. 15%) compared to steers fed CON. Increasing FE did not affect DMI, final BW, and ADG but tended (P < 0.09) to linearly improve G:F (150 to 157), and decreased (P= 0.03) incidence of abscessed livers (49 to 25%). Carcass traits were not affected by treatments. These results indicated that inclusion of wheat DDGS at 30% of the ration DM in finishing diets had adverse impacts on digestibility, feed efficiency and animal health. However, supplementing finishing diet containing wheat DDGS with FE potentially offset the negative effect of including wheat DDGS.
Keywords: feed efficiency, fibrolytic enzyme, finishing feedlot steers