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The mixture legume/grass determines agronomic advantages (i.e. lower N fertilization) and more equilibrate energy/N ratio in the forage for ruminant (Betti et al., 1992). In South of Italy, the most utilized intercropped forages are barley-fava bean and vetch-oats due to the particular climatic conditions.

The aim of the paper was to study the fermentation of the neutral detergent soluble fraction (NDS) using a 2x3x2 factorial arrangement of two intercropped forages (barley/broad bean and vetch/oats) collected at three growth stages and preserved by haymaking. Each feed sample and its isolated NDF were fermented in vitroand gas production was monitored utilizing the in vitrogas production technique (IVGPT). NDS gas yield was determined by the difference between gas from the unfractioned forage and that of its respective NDF. Haymaking decreased gas yield and rate of gas production from the unfractioned forage. Increasing maturi- ty did not change the final gas volume, but reduced the rate of gas production from the NDS fraction. The rate of gas production from the NDS fraction of hay decreased on average by 2.9 ml/h compared with fresh forage. On average, haymaking reduced the gas yield from the NDS fraction by 18.70%. The curve subtrac- tion technique can be used to study the effects of haymaking on the neutral detergent soluble fraction of for- ages.