Laboratory Analyses for Predicting Digestibility and Intake of Corn Silage1

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Abstract
High starch samples are difficult to filter using the neutral detergent fiber (NDF) method. Additional research is also required to identify the best in vitro dry matter disappearance (IVDMD) technique for prediction of in vivo digestibility of whole‐plant corn (Zea mays L.) forage. We designed experiments to compare methods of NDF and IVDMD determination for predicting in vivo intake and digestibility, respectively. In Experiment I, normal corn (105‐day maturity) harvested at five maturity stages (75% silk and 12, 24, 36, and 48 days later) was analyzed for NDF with and without amylase addition during refluxing. The standard deviation among triplicate samples was ±1.08 and ±0.56 for the unmodified and modified procedures, respectively. In Experiment II, normal and brown midrib corn of three maturity stages (75% silk and 24 and 60 days later) and mature (60 days) waxy and male sterile corn were analyzed using the treatments outlined above. In vivo digestibility was regressed on IVDMD dtermined by four methods (IVDMD, IVDMD + amylase, IVDMD + nitrogen, and IVDMD + NDF) and in vivo intake on NDF and NDF + amylase values. A greater percentage of variation in in vivo dry matter intake was explained when amylase was added (R2 = 96.0%) than when not (R2 = 52.0%). The addition of amylase to the in vitro fermentation vessel improved the prediction of in vivo dry matter digestibility (R3 = 67.2%) compared with the unmodified procedure (R2 = 53.3%).