Leaf and stem in vitro digestibility for grasses and dicotyledons of meadow plant communities in spring

The aim of this study was to improve prediction of the herbage digestibility of meadow plant communities rich in species. The variability of the in vitro dry matter digestibility (IVDMD) at a given date could result both from the species which constitute the plant community and from the variability in the proportion of the different plant components in relation to growth conditions. In order to separate the two factors, we studied the IVDMD change in spring, through the NIRS procedure, one month before and one month after the flowering stage of the main species. This was done for two sets of plant communities with very different botanical composition, dominated by species such as Dactylis glomerata and Chaerophyllum aureum (three) or Festuca rubra and Sanguisorba minor (two plant communities). The IVDMD of dicotyledons was higher than those of grasses both for leaf blades and for stems. The leaf blade IVDMD was quite stable throughout the period studied while those of grasses decreased by about 100 g kg -1 . The stem IVDMD for grasses as for dicotyledons first decreased quickly the month before the flowering stage of the main species, and then move slowly the next month. The difference in IVDMD between those species which were mostly in nutrient-rich habitats was 20 (stems of dicotyledons) to 80 g kg -1 (leaf blades of grasses) higher when compared to those species which were mostly in nutrient-poor habitats. These results, obtained for leaf blades and stems of sets of species with different habitat characteristics, were in agreement with those of the literature on swards which are almost always pure. For modelling the digestibility change for such plant communities through a growth period, we propose to use the IVDMD values characteristic of a given set of species, as outlined above, and the proportion of the different plant components in the herbage.