Effects of reconstituted finely ground corn grain or high-moisture rolled corn grain as replacers for finely ground dry corn grain when using a flint corn hybrid for lactating cows

The objective of this study was to evaluate the effects of replacing finely ground dry corn grain (DGC) with reconstituted finely ground corn grain (RCG) or high-moisture rolled corn grain (HMC) on nutrient intake, apparent partial and total-tract digestibility, rumen fermentation profile, milk yield and composition, and blood variables of dairy cows. A total of 9 Holstein dairy cows, 6 of which were rumen-cannulated, with mean (±SD) BW of 639 ± 15.1 kg, milk production of 30.4 ± 1.58 kg/d, parity of 2.2 ± 0.54, and DIM of 100 ± 10.7 were blocked for milk yield and DIM. They were then randomly assigned to a treatment sequence in a replicated 3 × 3 Latin square design. Three treatments were evaluated: (1) DGC, (2) RCG, and (3) HMC. Treatments accounted for 16% of the DM-based diet. The same flint corn hybrid was used for all treatment diets. Finely ground dry corn grain and RCG were ground through a 3-mm sieve, aiming for a final geometric mean particle size of less than 1 mm, and HMC was processed with a roller mill, aiming for a final particle size of less than 3 mm. Reconstituted finely ground corn grain and HMC were ensiled for 258 d and had DM contents of 58.4% and 49.5%, respectively. The diets contained approximately 22% DM-based starch. Intakes of DM, CP, NDF, undigestible NDF, starch, and ether extract were greater in HMC compared with DGC. The ruminal flow of DM was greater for both RCG and HMC compared with DGC. No effects were observed for ruminal digestibility and total-tract apparent digestibility of DM, NDF, and starch among treatments. However, the total-tract apparent digestibility of CP was greater for both RCG and HMC compared with DGC. Acetate and propionate concentrations (mmol/dL) were greater in cows fed RCG compared with DGC, whereas butyrate tended to be greater in cows fed HMC than in those fed DGC. A tendency for greater milk yield and ECM was observed for HMC compared with DGC. For milk solids, a greater fat content was observed in RCG and HMC compared with DGC. Feed efficiency (kg milk/kg DMI) did not differ among treatments. Given the overall similarity among the analyzed variables across treatments, the selection of a corn grain processing method should consider practical aspects beyond animal performance. Ensiled grains require a minimum storage period before use, which introduces logistical and management challenges, as well as potential DM losses during storage.