The objective of this study was to evaluate rumen microbiota of four adult male sheep, castrated, with rumen cannula, alloted in a randomized split-plot block design. The animals were fed Brachiaria decumbens hay diet, with increasing levels (0.5, 1.0 and 2.0 g/kg BW) of supplement with maize, soybean meal, urea and mineral mixture. The rumen fluid samples were collected from animals during fasting and at 2, 4 and 6h after feed, and analyzed immediately after the collection, for the parameters

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... H, methylene-blue reduction, cellulose digestion, activity and counting of ciliate protozoa (cel/mL). The pH values lower and higher than 7.0 were found during fasting (0h) and 2h after feed, respectively. The population of ciliated protozoa and its activity were higher at the highest supplementation level (P<0.05). At 0.5 g/kg BW level of supplementation, the population of protozoa decreased with the increase of pH, and greater number of protozoa /mL in rumen fluid was observed during fasting. Cellulose digestion and methylene-blue reduction were not affected by the treatments or after-feed hours (P<0.05). It was concluded that, during fasting, the increasing levels of supplementation affected positively the population of ciliated protozoa in the rumen but did not influence the bacterial activity.