This experiment compared the effect of grazing versus indoors feeding of ryegrass, on the chewing behaviour and the physical damage done to the grass during ingestive mastication in dairy cows. Ingestive boli were collected on four cows fed at grazing or indoors in a triple reversal design. The cows ingested smaller boli (93.4 vs 142.2 g; P<0.01) at a slower rate at grazing compared to indoors feeding. The proportions of cell contents released during mastication and the proportions of particles in the boli shorter than 2 mm were noticeably higher at grazing compared to indoors feeding. The consequence could be a higher rate of ruminal digestion of grass at grazing compared to indoors feeding.