A rumen‐fistulated steer was used for the manual collection of samples of freshly swallowed herbage, in a grazing‐management experiment on a perennial ryegrass sward. Diurnal and seasonal changes in thein vitrodigestibility of the herbage selected by the grazing animal were studied under both strip‐ and continuous‐grazing methods of management.There was no appreciable change in digestibility as the sward was grazed down from upper to lower layers under strip‐grazing management in April and May. In June to October a within‐day fall in digestibility was found, much of which was attributable to an increase in the amount of old dead herbage grazed from the lower regions of the sward. Dead herbage taken in by the grazing steer was considerably lower in digestibility in August than in May. Thein vitrodigestibility of herbage samples, cut to ground level before and after grazing in a strip‐grazed treatment, fell markedly as the proportion of dead herbage in the sample increased, giving a high negative correlation.In a continuous‐grazing management there was no pattern of diurnal variation, and the seasonal variation in digestibility of the ingested herbage was less than in strip grazing. The implications of these results are discussed in relation to indirect methods of digestibility determination (faecal‐index technique), the measurement of herbage intake, and to some aspects of g