In vitro and in sacco determination of neutral detergent fibre digestibility of treated cereal straw

Background Cereal straw is hardly digestible due to its complex bonds of lignin, cellulose and hemicellulose. That is why chemical treatments, such as with sodium hydroxide, may help to loosen the bonds and thus increase ruminal digestibility. Neutral detergent fibre ( NDF ) digestibility is a good predictor of feed intake. Therefore, in vitro methods have been developed to enhance the analytical throughput. The question was how well in vitro values of treated straw (oat, barley, wheat; 0, 15, 30 g NaOH /kg) obtained at 30 and 48 h of incubation correlate with in sacco values of cannulated cows after 30, 48 and 240 h. Results The treatment decreased the NDF and acid detergent fibre ( ADF ) concentration in the organic matter (OM). Increasing amounts of NaOH increased the NDF digestibility (NDFD) independent of method and incubation time. The ranking of straw type, however, was not consistent. The most serious difference was that the NDF degradation in sacco required many times over in vitro. Conclusion In vitro NDFD after 48 h of incubation correlated best with in sacco values achieved after 240 h and shall thus be used for cereal straw analysis.