The objective of this study was to investigate the effects of pre-grinding super-conditioning in comparison with steam flaking of corn on performance of Holstein dairy cattle in early lactation. Eighteen dairy cattle (milk yield 46.7±3 kg and DIM 131.6±14 d) were randomly assigned to one of three experimental diets: (1) concentrate containing of 50% pre-grinding super-conditioned corn (PSC; moisture 20%, retention time 6 min and conditioning temperature 95 °C); (2) concentrate containing of 50% steam flaked corn (SF; moisture 20%, retention time 60 min, rolling temperature 105 °C); and (3) concentrate containing of 50% grounded corn (G; 3 mm mill screen). Statistical analysis was performed using the GLM procedure based on completely randomized design of SAS (P<0.05). Geometric mean particle size and peNDF were increased (P<0.05) with SF corn than others. Dry matter intake, feed efficiency, DM, OM and ADF digestibility were not affected using experimental diets, but CP, starch and EE digestibility were increased (P<0.05) and NDF digestibility was decreased (P<0.05) in PSC than others. Rumen fluid pH, total VFA and molar proportions of acetate, propionate and butyrate were not different among diets, but ammonia nitrogen was decreased (P<0.05) in PSC than others. The pH and manure score were not affected, but the excretion of starch from faeces decreased (P<0.05) in PSC than others (0.61, 1.35 and 9.83% in PSC, SF and G, respectively). Milk yield was not affected using processed corn, but was 2 kg higher in PSC than SF and G corn. Milk fat content was shown a low tendency in PSC, but milk protein content was increased (P<0.05) in PSC than others. Milk fat to protein ratio was decreased (P<0.05) in PSC than other processed corn. It is concluded that pre-grinding super-conditioned corn in diet of early lactation dairy cattle increased of starch digestibility, milk production and efficiency of starch utilization and decreased starch excretion from faeces.

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