Effect of maize kernel endosperm type and maturity stage on ruminal in situ degradability and post-ruminal in vitro dry matter and starch digestibility

The objective of this study was to evaluate the interaction effect of maize grain texture (dent vs semi-flint) and two different stages of maturity (1/2 vs 3/4 milk line) on ruminal starch degradability and total tract digestibility using in situ and combined in situ-in vitro methods, respectively. The content of whole plant dry matter was 324.6 vs 399.5 g/kg (1/2 vs 3/4 milk line, respectively) for dent maize and 330.2 vs 401.3 g/kg for semi-flint maize. Organic nutrients (neutral detergent fibre, crude protein, ether extract, starch), 1000-grain weight, vitreousness, and mean particle size were determined. The evaluation was performed using two non-lactating Holstein cows fitted with ruminal cannulae. Effective degradability of dry matter and starch was calculated at ruminal outflow rates of 4, 6, and 8%/h. Vitreousness was lower for dent than for semi-flint grain, averaging 65.6% and 74.3% (P < 0.001). Ground dent maize grain showed lower mean particle size than did that of semi-flint maize (1.76 vs 1.88 mm, respectively, P < 0.001). Effective starch degradability calculated for the medium outflow rate (6%/h) was 69.1% vs 65.3% (P < 0.01) for dent and semi-flint maize and 69.0% vs 65.4% (P < 0.01) for lower (1/2 milk line) and higher (3/4 milk line) maturity, respectively. Higher (P < 0.001) mean starch total tract digestibility was found for dent maize (88.5%) than for semi-flint maize (82.5%) and for kernels harvested at 1/2 milk line (87.4%) than for those harvested at 3/4 milk line (83.6%, P < 0.001). Small differences in grain texture and silage maturity stage significantly influenced ruminal in situ degradability and total tract in situ-in vitro dry matter and starch digestibility.