Variation in cell wall digestibility of perennial ryegrass at heading stage

Perennial ryegrass (Lolium perenne) is the dominant forage grass in Europe, because of its high yield level, good persistence, high protein content and energy value. As high levels of water soluble carbohydrates (WSC) lead to rumen acidosis, the energy contained within the cell walls, which is released more gradually, has become a focus in ryegrass breeding. We have assessed the cell wall digestibility (NDFD) of blade, sheath and stem fraction of a set of 13 genotypes harvested at heading stage. Significant genotype-to-genotype differences were found for total plant NDFD, with genotypes explaining 68 % of the total variation. The observed variation in NDFD for sheath and stem was higher than for the total plant, with genotypes explaining 79 and 80 % of the total variation in sheath and stem NDFD respectively. Further, multiple linear regression showed that sheath NDFD, stem NDFD and the weight of the leaf fraction have a significant impact on the total plant NDFD values, whereas blade NDFD does not. Analysis of this limited set of genotypes has revealed limited variation in NDFD at the plant level, but a significant variation in organ fractions and organ-specific NDFD values, indicating potential selection targets to improve cell wall digestibility at the whole plant level.