Variation of digestibility in Italian ryegrass (Lolium multiflorum Lam. var. italicum Beck)

Among the NW-European fodder grass species Italian ryegrass has the highest yield potential when mown in short-term leys of up to 2 years. However Italian ryegrass is less digestible in the years after the seeding year than perennial ryegrass because of the presence of stems in almost all cuts. We compared digestibility components of vernalized perennial and Italian ryegrass. Italian ryegrass has a slightly lower content of water soluble carbohydrates (WSC) and its cell wall digestibility (NDFD) is much lower, especially in the summer cuts. In order to evaluate the possibility for improvement of the digestibility of Italian ryegrass by breeding we analyzed the variation of digestibility of plot trials sown with varieties and half-sib families of Italian ryegrass. The variation of the NDFD among vernalized families of Italian ryegrass is similar to the variation of the organic matter digestibility (OMD) but much lower than the variation of the content of WSC. The OMD is better correlated to NDFD than to WSC. The variation in NDFD is higher in summer cuts than in spring and autumn cuts. There is no correlation between NDFD and dry matter yield or crude protein content. We may conclude that there is scope for the improvement of the digestibility of Italian ryegrass by breeding for higher cell wall digestibility of the herbage in summer cuts.