Use of 30-hour in vitro neutral-detergent-fiber digestibility of feedstuffs in dairy ration-formulation software: Evaluation of predictions for milk and methane production in lactating dairy cows

ABSTRACT Objective Our objective was to determine whether the use of 30-h in vitro NDF digestibility (NDFD30) of fibrous ingredients included in rations fed to lactating dairy cattle improves the accuracy of milk and CH4 production predictions from the Cornell Net Carbohydrate and Protein System (CNCPS, v. 6.5). Materials and Methods Animal performance from 8 energy-balance studies were compiled into a database along with the treatments fed during those studies. Observed animal performance was compared with milk and CH4 predictions from CNCPS (v. 6.5) when using CNCPS feed library NDF rate of digestion (kd) values or when using NDF kd calculated from NDFD30. The in vitro analysis was conducted according to Goering and Van Soest (1970) , and ash-free, α-amylase-treated NDF of the residue was determined according to methods outlined by Mertens (2002) . Results and Discussion Predictions of milk production were poorer with use of NDFD30, the concordance correlation coefficient decreased from 0.87 to 0.82 and mean bias increased −0.23 to 1.30 kg. Methane production predictions were unaffected with use of NDFD30. The concordance correlation coefficient increased from 0.33 to 0.38, but slope and mean bias were similar. These results indicate that including NDFD30 to estimate the kd of NDF may not improve ME allowable milk or CH4 production predictions when using the CNCPS ration model. Implications and Applications Our results suggest that milk production predictions from CNCPS (v. 6.5) are reliable but CH4 predictions can be improved. Including NDFD30 did not provide additional value to ration formulation because it did not improve milk or CH4 production predictions. The next steps should evaluate including more time points, such as 30, 120, and 240 h in vitro, to determine whether altering the total pool of potentially digestible NDF and the rate of NDF digestion would improve predictions from CNCPS.