Two leafy strains of cocksfoot, S143 and S37 were subjected to winter, spring and winter + spring defoliation; 2 cwt. per acre of nitro‐chalk was applied after each defoliation, in addition to the standard manuring for all plots.Winter grazing of leafy cocksfoot does not appear to depress the yield of seed appreciably when extra nitrogen is applied.Grazing of cocksfoot in mid‐April is likely to depress the seed yield substantially, especially if followed by a very dry summer.The reaction to hard defoliation by sheep may vary with the growth form of the cocksfoot strain.Grazing appeared to be more detrimental to seed yield than defoliation by cutting.During this investigation, prolonged frost which occurred during the early part of the year appeared to have an adverse effect on cocksfoot seed yi