The effect of feeding indoors fresh perennial ryegrass vs. grazing on ingestive behaviour, release of cell contents and comminution of particles during ingestion, as well as on gas production of ingested boli fermented in vitro, was studied. Indoor feeding and grazing were compared using four dairy cows according to a triple reversal design with six periods. Chemical and morphological composition of the ingested herbage was similar for both indoor feeding and grazing treatments. The intake rate was markedly higher indoors compared with grazing [52AE1 vs. 22AE9 g dry matter (DM) min )1 ] with heavier boli and less saliva added per gram of DM intake. The proportions of intracellular nitrogen and chlorophyll released during mastication after ingestion of herbage fed indoors were lower, and the median size of the particles in the boli was larger (5AE97 vs. 4AE44 mm) compared with grazing. As a result, the rate of gas production in vitro was also lower for herbage fed indoors compared with grazing (0AE423 vs. 0AE469 mL min )1 g )1 incubated DM). Indoor feeding or grazing may have limited consequences in vivo on the kinetics of availability of nutrients for micro-organisms in the rumen, because the consequences of the more extensive physical damage suffered by herbage ingested at grazing could be compensated by a lower intake rate.
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.
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