LEAF AND STEM NUTRITIVE-VALUE OF TIMOTHY CULTIVARS DIFFERING IN MATURITY

The nutritive value of herbage is a function of the nutritive value of its component leaves and stems and their proportion in the herbage. A previous study indicated that the proportion of leaves in the herbage did not explain entirely the differences in in vitro true digestibili ty and NDF concentrations between early and late-maturing timothy (Phl eum pratense L.) cultivars. It was therefore hypothesized that the lea ves and stems of early and late-maturing cultivars differ in nutritive value. The evolution of leaf and stem nutritive value of field-grown timothy cultivars differing in maturity, and the relationships between parameters of leaf and stem nutritive value, and the leaf to weight r atio (LWR) were studied during primary growth in two experiments. On a given date, stems of early-maturing cultivars had in vitro true diges tibilities of dry matter and cell wall up to 61 g kg(-1) DM and 71 g k g(-1) DM lower that those of late-maturing cultivars, respectively. Th e NDF concentration of stems of early-maturing cultivars was up to 32 g kg(-1) DM greater than that of late-maturing cultivars. There were n o cultivar differences in leaf in vitro true digestibilities of dry ma tter and cell wall, and NDF concentration on a given date. At a given LWR, however, the leaves and stems of early-maturing cultivars had gre ater in vitro true digestibilities of dry matter and cell wall, and a lower NDF concentration than those of late-maturing cultivars. Our res ults indicate that differences in herbage nutritive value at a given s tage of maturity between early- and late-maturing timothy cultivars is explained by a greater nutritive value of leaves and stems of the ear ly-maturing cultivars.