It is shown that the available energy, T.d.n. or S.e., contained in the dry matter of Kenya pastures at all stages of growth is remarkably constant. Thus in the early stages of growth of such pastures when the available D.c.p. is present in amounts suitable for very high milk yields the available energy limits their attainment. During later growth, as the amount of C.p. in the pasture becomes increasingly diluted by carbohydrate there is a progressive decrease in amount of available D.c.p. and it in turn becomes inadequate to sustain the original limited level of productivity.