Previous research with roughage and wet distillers grains with solubles (WDGS) concentrations in feedlot diets based on steam-flaked corn has not extensively evaluated measurements of digestibility. Two experiments were conducted to evaluate the effects of concentrations of alfalfa hay (AH) and WDGS on apparent total-tract nutrient digestibility by finishing cattle and in vitro fermentation characteristics. In both studies, treatments were arranged in a 2 × 3 + 1 factorial and consisted of diets based on steam-flaked corn including AH (6 or 12% of DM) and WDGS (15, 30, or 45% of DM), and a control diet without WDGS that contained 9% AH. In Exp. 1, 56 beef steers (initial BW = 395 ± 7 kg) were used in a randomized complete block design and fed for 28 d. Intakes of DM, OM, NDF, ADF, and CP were greater (P ≤ 0.048) by steers fed 12 versus 6% AH. Increasing the dietary concentration of WDGS increased NDF, ADF, and CP intakes (P ≤ 0.046), and an AH × WDGS interaction (P ≤ 0.02) was detected for starch intake. Digestibility of DM and OM was greater for control steers than for the average of all treatments containing WDGS (P < 0.01). In Exp. 2, ruminal fluid was collected from 2 ruminally cannulated steers adapted to a 60% concentrate diet to evaluate in vitro total gas and methane production, nutrient disappearance, and VFA concentrations after 24 h of incubation. Total gas production decreased linearly as WDGS increased (P = 0.04). The control substrate had decreased NDF disappearance versus the average of other treatments (P < 0.01), and consistent with in vivo total-tract digestibility, in vitro NDF disappearance increased linearly as WDGS increased (P < 0.01) regardless of AH concentration. The concentration of AH and WDGS in feedlot diets had interactive effects on total-tract digestibility of DM, OM, and starch, but not NDF, in feedlot steers.
- alfalfa hay
- wet distillers grains with solubles