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

For modelling of grass digestibility throughout the growing season, the imp act of cutting on individual leaves needs to be quantified. Therefore, at g lasshouse experiment was carried out with Italian ryegrass (Lolium multiflo rum Lam) grown from seed. Waif of the plants were grown undisturbed until l eaf stage 8, while the other half were cut at leaf stage 4, after which the y were allowed to grow until leaf stage 9. The composition and digestibilit y characteristics of leaves 6, 7 and 8 on the main shoot of plants from bot h treatments were quantified. In the uncut plants, leaf blade length and ma ss and specific cell wall (CW) and organic matter (OM) mass (mgcm(-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 DMcm (-2)). Leaf 6, that was damaged by cutting, showed a lower initial CW conte nt and a rapid decline of specific CW and OM mass and of digestibility duri ng ageing. Its low specific mass and digestibility of CW could have been re lated to cessation of CW synthesis during its growth after cutting, its was evidenced by the lower CW thickness of sclerenchyma cells. The later-forme d leaves, 7 and 8, had digestibility characteristics similar to those of th e uncut plants. Since leaf 6 hardly contributed to the total plant dry matt er mass, the cut and the uncut plants differed only slightly in digestibili ty of the total leaf fraction. It can be concluded that cutting sets back l eaf size and growth rate but has little effect on digestibility characteris tics during ageing. (C) 1999 Society of Chemical Industry.