This study aimed to 1) evaluate the interaction of corn grain micronization and starch levels per meal on equine plasma glucose, and 2) determine if micronization affects the risk of hindgut acidosis. Six mature (aged 6 to 10 years), healthy, non-pregnant mares (initial body weight [BW]: 301 to 463 kg) were used in a 2×3 factorial cross-over design. The treatments included two forms of corn grain (ground and micronized flaked) at three levels of starch (1, 1.5, and 2 g/kg BW per meal). The blood was sampled before and 30, 60, 90, 120, 180, 240, and 300 min after morning feeding and the glucose concentration in the plasma was determined. Small intestine and hindgut dry matter (DM) disappearances of ground and micronized corn were also compared using in vitro techniques. Micronized flaked corn grain showed three times more in vitro enzymatic DM disappearance (P < 0.001) compared with ground corn. Residues of in vitro enzymatic digestion of micronized flaked corn fermented 38.59 % faster than ground corn during in vitro hindgut incubation. The horses that consumed micronized flaked corn had higher post-prandial plasma glucose concentrations (P < 0.001). Increasing starch levels per meal from 1-2 g/kg BW resulted in higher plasma glucose concentrations (P = 0.005). However, no interaction of processing and starch meal size was found. Overall, processing the corn grain by micronization or increasing starch level per meal increased the plasma glucose concentrations, but the magnitude of the increases did not match that expected from in vitro studies

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