Abstract
Orchardgrass (cv, kitamidori), tall fescue (cv, hokuryo) and timothy (cv, senpoku) were cut at the first week and 2nd week after the date of first heading from 1979 to 1981. Tillers of each species were classified into three groups, booting, heading and vegetative tillers. Distribution ratio of classified tillers and in vitro dry matter digestibility (IVD) of those tillers were determined. IVD of field grasses (a mixture of different growth stage tillers), the distribution ratio of classified tillers and IVD of those tillers varied with the year. Annual variations in IVD of the field grasses were influenced by the differences in distribution ratio of tillers and changes in ambient temperature. Only heading tillers of the above species in a fixed area were cut at 3-day intervals during the heading period in 1982. Relationship between the number of days from May 1 till cutting (X1) and 3-day daily mean ambient temperature before cutting (X2 ; ℃) to variation of IVD (Y ; %) of heading tillers were investigated by multiple regression analysis. Significant relationships between variables were as follows : regarding three species in a lump, later heading tillers were lower in IVD than earlier ones, viz., partial correlation coefficients (PCC) of X1 and of X2 were - 0.977 and - 0.541, and standard partial regression coefficients (SRC) of X1 and of X2 were - 0.966 and - 0.135, respectively. In the case of timothy, changes in IVD of heading tillers were associated with both X1 and X2, viz., PCC of X1 and of X2 were - 0.994 and - 0.991, and SRC of X1 and of X2 were - 0.887 and - 0.727, respectively. Relationship between IVD and chemical components of heading tillers (Exp. in 1982) were as follows : cell wall constituents (CWC), acid detergent fiber and acid detergent lignin contents of orchardgrass increased with the decrease in IVD. No such relationship was observed in the case of tall fescue and timothy, and CWC contents of those species were not correlated with IVD.
