The nutritive values of grass silages made with delayed sealing of the silo were compared with those of silages made by ensiling directly, and with dried grass. First and third cut materials of different composition were used in two separate experiments each with nine rumen‐fistulated sheep. Silages made with direct sealing of the silo had higher digestibilities of dry matter, organic matter and nitrogen than materials made with delayed sealing which, in turn, had higher digestibilities than dried grass. Metabolisable energy content was higher but intake of dry matter lower with the directly ensiled material so that delayed sealing of the silo resulted in a greater intake of metabolisable energy. The effect of delayed sealing on the major ruminal volatile fatty acids wasdifferent for first and third cuts. Comparison of ruminal non‐glucogenic ratios for silages made from first cut grass indicated that the energy of the material made with delayed sealing would be more efficiently utilised than that produced by direct sealing. With the third cut material the position was reversed. The metabolisable energy of autumn grass was likely to be less efficiently used than that of spring cut material.