Laboratory Evaluation of Corn Grain and Silage Digestibility

The primary objective of this trial was to compare commercially available laboratory assays for assessing starch digestibility of dry (DC) and high-moisture (HMC) corn and corn silage (WPCS) using samples from 22 dairy farms. In addition, in vitro NDF digestibility (IVNDFD) in WPCS was measured at 2 incubation times (24 and 48 h). Dry matter contents of HMC and WPCS were 73.7 ± 3.7% and 35.8 ± 4.7%, respectively. The r-value from multiple regression of degree of starch access (DSA) on DM content and mean particle size for HMC was 0.78 (P < 0.0001). Dry matter content was negatively (r = - 0.66) correlated (P < 0.05) to a modified in vitro ruminal plus intestinal starch degradation assay (MIVSD-RI) in HMC, but MIVSD-RI was not related (P > 0.10) to mean particle size for either HMC or dry corn. For WPCS, DSA was positively but not highly (r = 0.43) correlated (P < 0.05) with kernel processing score. The MIVSD-RI of WPCS varied minimally (98.0 ± 1.1% of starch) and was greater than DSA (93.7 ± 2.3% of starch). Average 24-h IVNDFD was 19 percentage units lower than average 48-h IVNDFD for WPCS. The r-value from regression of 24-h IVNDFD on 48-h IVNDFD was only 0.57 (P < 0.05). More comparative research of assays designed to assess starch and NDF digestibility and further research to validate results relative to in vivo digestibility data is needed. Additionally, more research on the relationship of 24- to 48-h IVNDFD and to NDF digestion and DMI is needed.