The experiment was performed to evaluate plasma urea nitrogen (PUN) level of crossbred cows under two rotational grazing areas, one of elephantgrass cv. Guaçu (Pennisetum purpureum Schum. cv. Guaçu) and other one of Tanzaniagrass (Panicum maximum Jacq. cv. Tanzania). Forage production, stem, leaf and dead material were also evaluated, on dry matter basis (DM), as well as the crude protein (CP) and neutral detergent fiber (NDF) in the forage samples. Blood was collected four times, using 16 cows for grass species. The average of pre grazing forage mass was 5321 and 5384 kg of DM/ha by grazing cycles for elephantgrass and Tanzaniagrass. The forage disappeared after grazing, as leaf, stem and dead material was 1400, 620 and 443 kg of DM/ha for elephantgrass and 1586, 736 and 132 kg of DM/ha for Tanzaniagrass, by grazing cycle. The averages of CP and NDF in the forage samples during four grazing cycles in the stem, leaf, dead material and residue were 8.4, 78.5, 6.9, 77.1, 12.5, 76.3, 5.3, 82.6, 6.5, 80.2, respectively, for elephantgrass and 9.3, 81.6, 7.4, 82.4, 14.3, 80.4, 6.3, 82.9, 7.6, 81.6, respectively, for Tanzaniagrass. Significant difference was observed for PUN levels of cows fed different grass species and for time of sampling of the blood. The averages of PUN were 9.8 mg/dL for the cows grazing elephantgrass and 10.6 mg/dL for the cows grazing Tanzaniagrass. The low levels of PUN reflect low level of crude protein ingestion, for cows grazing tropical pastures.
crude protein; neutral detergent fiber; Panicum maximum Jacq. cv. Tanzania; Pennisetum purpureum Schum
