Increasing the digestibility of grass silage by harvesting grass at an earlier stage of growth has been shown to produce major increases in the intake and performance of beef cattle providing the increase in digestibility has not been accompanied by poorer fermentation. However there is considerable variation in the recommended optimum dates for harvesting primary growths depending on the variety type of the grass.

Two experiments have been carried out to examine the interaction between ryegrass variety type and date of harvesting for silage. Two replicate swards containing equal proportions of three early-heading varieties (Cropper, Premo and Frances) (50% ear-emergence on 19 May) were harvested on 20 May (Tl), 28/29 May (T2) and 5/6 June (T3) and two swards containing equal proportions of three late-heading varieties (Perma, Preference and Parcour) (50% ear-emergence on 12 June) were harvested on 28/29 May (T4), 5/6 June (T5) and 12/14 June (T6) in 1985 and 1987. In experiment 1 the swards for the six silages were cut with a rotary mower, lifted with a precision-chop forage harvester within 15 minutes of being mown, and ensiled in trench silos. Formic acid was applied at a rate of 2.5 1/t fresh grass. In experiment 2 the swards were harvested directly using a double-chop forage harvester and the herbages were ensiled without the addition of an additive.