Composition and digestibility during ageing of consecutive leaves on the main stem of Italian ryegrass plants, growing undisturbed or regrowing after cutting

For modelling of grass digestibility throughout the growing season, the impact of cutting on individual leaves needs to be quantified. Therefore, a glasshouse experiment was carried out with Italian ryegrass (Lolium multiflorum Lam) grown from seed. Half of the plants were grown undisturbed until leaf stage 8, while the other half were cut at leaf stage 4, after which they were allowed to grow until leaf stage 9. The composition and digestibility characteristics of leaves 6, 7 and 8 on the main shoot of plants from both treatments were quantified. In the uncut plants, leaf blade length and mass and specific cell wall (CW) and organic matter (OM) mass (mg cm(-2)) was higher for consecutive leaves. During leaf ageing specific CW mass remained unchanged, while specific OM mass and CW digestibility declined, resulting in a decline of OM digestibility. CW digestibility of leaves decreased to c 78%, a value also found in an earlier experiment. The newly formed leaves after cutting had a reduced leaf size and specific leaf mass (SLM, mg DM cm(-2)). Leaf 6, that was damaged by cutting, showed a lower initial CW content and a rapid decline of specific CW and OM mass and of digestibility during ageing. Its low specific mass and digestibility of CW could have been related to cessation of CW synthesis during its growth after cutting, as was evidenced by the lower CW thickness of sclerenchyma cells. The later-formed leaves, 7 and 8, had digestibility characteristics similar to those of the uncut plants. Since leaf 6 hardly contributed to the total plant dry matter mass, the cut and the uncut plants differed only slightly in digestibility of the total leaf fraction. It can be concluded that cutting sets back leaf size and growth rate but has little effect on digestibility characteristics during ageing.