Impact of flint corn processing method and dietary starch concentration on finishing performance of Nellore bulls

Nellore cattle are predominant in Brazil and appear to have poor performance when fed high-grain diets. In addition, most corn produced in Brazil is of the flint type, and the starch therein is more difficult to digest compared to that in dent corn hybrids. The aim of this study was to evaluate flint corn processing method (CPM) and dietary starch content for finishing Nellore bulls fed high-concentrate, corn-based diets. In this study, 112 Nellore bulls (initial BW 378.3 ± 21.28 kg) were fed twice daily using Calan gates or individual pens. The animals were used in a randomized complete block design with a 2 × 4 factorial arrangement of treatments. The experiment tested two CPM: high moisture corn (HMC) and finely ground dry corn (FGC) and dietary starch concentrations (DSC) of 300, 350, 400 and 450 g/kg DM, replacing citrus pulp with corn. Bulls were adapted to finishing diets over a period of 18 days and fed a total of 75 days (18 + 57 days). To determine fecal starch (FS) concentration, feces from each animal were sampled on day 47 of the feeding period. Bulls fed diets containing more than 300 g/kg DSC from HMC were more efficient than bulls fed 300 g/kg DSC as HMC; but gain:feed ratio (G:F) for bulls fed FGC did not differ (CPM × DSC; P = 0.04). Final BW and average daily gain (ADG) were not affected by CPM, but carcass G:F was greater for bulls fed HMC than for those fed FGC (P < 0.01). Increases in DSC resulted in quadratic decreases in DM intake (P = 0.02), linear decreases in metabolisable energy (ME) intake (P < 0.01), and linear improvements in carcass G:F (P < 0.01). Interactions between CPM and DSC were observed for calculated dietary concentrations of net energy for maintenance (NEm), net energy for gain (NEg), and ME (P = 0.02), whereby NEm, NEg and ME of diets increased linearly with increases in DSC for bulls fed HMC, but did not differ across DSC for bulls fed FGC. Bulls fed FGC had 2.75 times greater FS compared to bulls fed HMC (P < 0.01); resulting in lower fecal pH for bulls fed FGC compared to those fed HMC (P < 0.01). In conclusion, there was no effect on G:F of Nellore cattle or net energy content of diets when DSC was increased by adding flint FGC, but increasing HMC in diets improved growth efficiency and net energy content.