We evaluated the grazing behavior of heifers, at two phenological stages (vegetative and reproductive) of ryegrass (Lolium multiflorum Lam.), in four times of the day (early morning, morning, evening, and night), with heifers either exclusively grazing or with oat, or corn grain, supplementation. The experimental design was completely randomized, in sub-subdivided plot arrangement, in which the main plots were the feeding systems, the sub-plots were the phenological stages and the sub-sub-plots were the times of day. We assessed ingestion behavior along 24 hours through visual observation, on four evaluation dates, two during the vegetative stage and two during the reproductive stage, studying time spent on grazing, rumination, or other activities, as well as number and duration of, and interval between meals. Supplemented heifers remained less time at a feeding station, performed fewer bites daily and, during the reproductive stage of the ryegrass, spent more time in other activities. Grazing time of supplemented heifers was shorter in the morning and at night, and the duration of their meals was shorter at night. A change occurred in the pattern of time use when heifers received supplement, and when the structural and qualitative characteristics of the pasture changed during the vegetative and reproductive phenological stages of ryegrass.