Variation of cell wall digestibility in fodder grasses and a perennial ryegrass breeding pool

Improved cell wall digestibility (NDFD: digestibility of neutral detergent fibre) of fodder grasses may contribute to a higher dry matter intake and a better grass protein use efficiency by the ruminant. We determined NDFD of several fodder grass species (perennial and Italian ryegrass, meadow and tall fescue, cocksfoot and timothy) and families of a perennial ryegrass breeding pool by NIRS (near infrared reflectance spectroscopy). Among the grass species perennial ryegrass had the highest and timothy the lowest mean annual cell wall digestibility. Tetraploid ryegrass varieties showed a higher NDFD than diploids. The variation of the NDFD among families of perennial ryegrass is similar to the variation of the organic matter digestibility (OMD) but much lower than the variation of the content of water soluble carbohydrate (WSC). The mean annual NDFD is signifi-cantly correlated with the NDFD of all single cuts but best with the NDFD of the last cut which also showed the largest variation. NDFD is positively correlated with OMD and negatively with the dry matter content. There was no correlation with WSC content. Because of the low variation of NDFD among families of perennial ryegrass when frequently cut, selection for higher digestibility by increasing NDFD will be hard.