the experiment was carried in inra (institut national de la recherche agronomique) at theix, france. two grasses (perennial ryegrass and tall fescue) were grown in sward boxes (0,13 m2) and submitted to three defoliation intervals (3,5, 7 and 14 days between two successive defoliation) and three defoliation intensities (160, 320 and 640 bites.m-2 at each defoliation). four months after sowing, at defoliation date, sward boxes were offered to four individual dry ewes and removed after a given number of bites had been taken. for each grass species, the growth, senescence and defoliation fluxes were studied. the results showed that the interval and the intensity of grazing had distinct effects on the growth, senescence and defoliation fluxes as well as on the equilibrium of grass mixtures.