Flint corn grain processing and citrus pulp level in finishing diets for feedlot cattle

摘要

Four trials were conducted to evaluate the effects of flint corn processing and the replacement of corn with citrus pulp (CiP) in diets for Nellore feedlot cattle. In a 103-d finishing trial, 216 Nellore bulls (350 +/- 24 kg initial BW) were used in a randomized complete block design with a 2 x 4 factorial arrangement of treatments. Factors included 2 processing methods, either ground corn (GC) or steam-flaked corn (FC), with CiP replacing each corn type at 4 levels (0, 25, 50, and 75% of DM). All diets contained 12% sugarcane bagasse and 88% concentrate (DM basis). Treatments were also evaluated in metabolism trials, in which 10 ruminally cannulated Nellore steers (389 +/- 37 kg) were assigned to 2 independent but simultaneous 5 x 5 Latin squares, each using 1 method of corn processing (GC and FC). Interactions (P < 0.05) between corn processing and CiP inclusion level were observed for final BW, DMI, ADG, G:F, and HCW. With FC-based diets, added CiP linearly decreased final BW (P = 0.04), whereas with GC-based diets, added CiP quadratically increased final BW (P = 0.002). With FC-based diets, the inclusion of CiP linearly increased DMI (P = 0.03) and linearly decreased ADG (P = 0.03) and G: F (P = 0.001). Increasing CiP in GC-based diets quadratically increased DMI (P = 0.001), ADG (P = 0.005), and HCW (P = 0.003). In FC-based diets, CiP inclusion had no effect on HCW (P = 0.21). Dressing percent, LM area, and 12th-rib fat were not affected by diet (P = 0.05). For steers fed GC diets, CiP inclusion in the diet quadratically decreased the molar proportion of isovalerate (P = 0.001) but linearly increased ruminal butyrate (P = 0.006). No differences (P >= 0.16) were observed for total VFA concentrations, acetate: propionate ratio, and ruminal NH3-N as CiP replaced GC. For steers fed FC diets, the molar proportion of acetate linearly increased (P = 0.002) whereas the proportion of propionate was linearly decreased (P < 0.001), resulting in a linear increase (P = 0.001) in the acetate: propionate ratio. Replacing corn with CiP linearly reduced NEm (P = 0.001) and NEg (P < 0.001) of FC-based diets but did not affect (P = 0.15) NE values of CG-based diets. Steam flaking flint corn improved cattle performance in this trial more than has been reported for dent corn in the published literature.