Effects of corn processing method and dietary starch level on finishing performance of Nellore bulls

Abstract Text: The objective of this study was to evaluate flint corn processing method (CPM) and level of starch for finishing Nellore bulls with high-concentrate, corn-based diets. Nellore bulls (n=112; 378.25 ± 21.28 kg) were used in a randomized complete block design in a 4 x 2 factorial arrangement. Four starch levels (30, 35, 40 and 45% of diet DM) were evaluated for two CPM: high moisture corn (HMC) and finely ground dry corn (FGC). Animals were offered ad libitum access to diets delivered twice daily in individual pens. Flint corn had 77.2% vitreousness, and corn geometric particle sizes were 1.30 and 5.84 mm for FGC and HMC, respectively. Bulls were adapted to the finishing diet over a 18 d period and fed a total of 75 d. To determine fecal starch (FS) concentration, each animal was sampled by rectal palpation on d 47 of the feeding period. The first derivative was solved of a 2^nd order polynomial to determine optimal dietary starch level (DSL). Interaction between CPM and DSL was observed for G:F (P=0.04). Animals fed HMC 35% up to 45% DSL were more efficient than those fed HMC 30% DSL. However, G:F for bulls fed FGC 30% up to 45% DSL had no difference. DMI was 13.6% greater for FGC than those fed HMC (P<0.01), but the final BW and ADG was not affected by CPM. Increases in the DSL resulted quadratic decreases in the DMI (P=0.02) and linear decreases in the ME intake (P<0.01). Interactions between CPM and DSL were found (P=0.02), bulls fed HMC showed a linear increase in NEm (P=0.02), NEg (P=0.02) and ME (P=0.02) when the DSL increased. However, NEm, NEg and ME for bulls fed FGC were not different with inclusions of DSL. Bulls fed HMC showed 2.75 times lower FS than those bulls fed FGC (P<0.01), consequently the fecal pH was greater for HMC than FGC (P<0.01). Fecal DM were 31.4% greater for FGC than HMC (P<0.01), consequently the density was greater for FGC feces than HMC (1.120 vs. 1.098 g/mL; P=0.02). In conclusion, HMC improved growth efficiency of Nellore cattle and the proportion of DSL required to optimize performance was dependent on CPM.

Keywords: feedlot, starch, zebu