Comparison of analyses to predict ruminal fibre degradability and indigestible fibre in temperate grass silages
The objective of this study was to compare the ruminal degradability of neutral detergent fibre (NDF) and indigestible NDF (INDF) between silages (n = 24) that originated from three different temperate grass species, i.e. Dactylis glomerata L., Festuca arundinacea L. and hybrid, Felina – Lolium multiflorum L. × Festuca arundinacea S. The data is used to create prediction equations for the effective degradability of NDF (EDNDF), assuming ruminal solid outflow rates of 0.02 (low), 0.05 (medium) and 0.08/h (high), and INDF. The highest values for the potentially degradable fraction of NDF (b), EDNDF2, EDNDF5 and EDNDF8 (874, 560, 366 and 272 g/kg NDF, respectively) and the lowest for INDF (73.1 g/kg DM) were found for F. arundinacea. These parameters were significantly different from the hybrid Felina, which presented the lowest rate of NDF degradation (c), EDNDF5 and EDNDF8 (0.033/h, 341 and 250 g/kg NDF, respectively). The highest for c (0.038/h) and INDF (86.9 g/kg DM) and the lowest for b (847 g/kg NDF) were detected for D. glomerata. The combination of acid detergent fibre (ADF) and acid detergent lignin (ADL) (R2 = 0.844) were identified by a backward, stepwise, multiple regression analysis as the most accurate to predict INDF. Crude protein, ADF and NDF were found as the most suitable combination for predicting EDNDF2 (R2 = 0.715), EDNDF5 (R2 = 0.669) and EDNDF8 (R2 = 0.648). Calculated equations found practical application in laboratory analyses to evaluate the nutritional quality of feeds for ruminants.
Keywords: Grass silage, neutral detergent fibre, rumen degradation, prediction equations