Interactive effects of bulk density of steam-flaked corn and concentration of sweet bran wet corn gluten feed on feedlot cattle performance, carcass characteristics, and apparent total tract nutrient digestibility

Two experiments were used to evaluate the interactive effects of varying bulk density (BD) of steam-flaked corn (SFC) and concentration of wet corn gluten feed (WCGF; Sweet Bran, Cargill Corn Milling, Blair, NE) on feedlot performance, carcass characteristics, and apparent total tract digestibility. In Exp. 1, 108 yearling steers (initial BW = 367 ± 1.2 kg) received 1 of 3 different SFC BD treatments in a randomized complete block design. Bulk density treatments were 283, 335, or 386 g/L SFC in diets containing 25% WCGF (% of DM). In Exp. 2, two hundred twenty-four steers (initial BW = 367 ± 1.6 kg) were used in a 2 × 3 + 1 factorial arrangement of treatments. Experimental diets consisted of 0, 15, or 30% WCGF (DM basis) with a BD of SFC at 283 g/L (0-22, 15-22, or 30-22) or SFC at 360 g/L (0-28, 15-28, or 30-28). The additional treatment consisted of 15% WCGF, SFC at 283 g/L, and a decreased inclusion of alfalfa hay at 6% (15-28-6) vs. 9% alfalfa hay for all other treatments. In both Exp. 1 and 2, steers were fed once daily to provide ad libitum access to feed for an average of 163 d. In addition, both experiments had a 5-d digestion period in which DMI was measured and fecal samples were collected from each pen for measurement of nutrient digestibility using dietary acid insoluble ash as a marker. In Exp. 1, varying BD of SFC did not affect (P ≥ 0.24) overall DMI, ADG, or G:F on a live- or carcass-adjusted basis. Dressing percent and LM area increased linearly (P ≤ 0.05) as bulk density increased, but other carcass traits were not affected by treatments. Intake of DM, OM, and CP during the digestion phase did not differ among bulk BD; however, starch intake increased linearly (P = 0.004) as BD of SFC increased. Digestibility of DM, OM, and CP tended (P ≤ 0.065) to decrease, and starch digestibility decreased linearly (P = 0.002) as BD of SFC increased. In Exp. 2, except for interim measurements for G:F and calculated NE values, there were no WCGF × BD interactions feedlot performance, carcass characteristics, and few differences in digestibility. Similarly, contrasts between 15-28 and 15-28-6 also yielded few differences for performance and carcass data. Live and carcass-adjusted final BW responded quadratically (P ≤ 0.02) to WCGF inclusion, and both increased (P ≤ 0.007) BW with greater BD. As WCGF inclusion increased, G:F and calculated NE values decreased quadratically (P ≤ 0.03). Steers consuming 360 g/L SFC had greater (P < 0.05) G:F than those fed 283 g/L SFC. Hot carcass weight, marbling score, 12th-rib fat thickness, and calculated yield grade increased quadratically (P ≤ 0.04) with increased inclusion of WCGF. In addition, percentage of cattle grading Premium Choice or greater responded quadratically (P = 0.04) to WCGF concentration. Greater BD increased (P ≤ 0.01) HCW, dressing percent, marbling score, 12th-rib fat thickness, and decreased calculated yield grade and percentage of cattle grading USDA Select; however, lower BD tended (P = 0.09) to increase LM area. Intake of DM, OM, CP, and NDF and fecal output during the digestibility period increased linearly (P ≤ 0.01) with increasing WCGF, and greater BD increased (P ≤ 0.04) intake of DM, OM, starch, and CP. Digestibility of starch decreased quadratically (P = 0.008) as WCGF increased; however digestibility of CP and NDF increased linearly (P ≤ 0.02) with greater concentrations of WCGF. The 283 g/L BD increased (P ≤ 0.02) starch and CP digestibility compared with 360 g/L. These data suggest that increasing BD of SFC and increasing WCGF inclusion can yield equal or greater performance and carcass characteristics to diets containing SFC of lesser BD and diets without WCGF; however, increasing WCGF and BD in finishing diets might not be ideal for starch digestibility.