The work aimed to evaluate the effect of the irrigation on the production of biomass and the nutritional value of Panicum maximum, Jacq. cv. Mombaça and Pennisetum purpureum Schum, cv. Napier. Four treatments were tested, consisting of the combination of irrigation levels and two forages. A split-plot arrangement in time and space in a complete randomized block design was used, with more than one observation per treatment, per block. The forages were evaluated under rotational stocking, using F1 European-zebu steers, with average body weight (BW) of 260 kg. It was used a variable stocking technique and target herbage allowance was 4 kg leaf dry matter per 100 kg animal BW. Total and green DM availabilities were greater for napiergrass than for mombaçagrass, being observed the same pattern for the irrigation effect. The forages did not differ regarding the leaf DM (LDM) availability. Irrigation increased LDM availability. Mombaçagrass showed higher DM concentration. The forages did not differ regarding the concentration of CP, OM, ash, NDF and ADF in DM, which were also not affected by irrigation. Mombaça-grass showed higher in vitro DM digestibility (IVDMD). Regression analysis showed linear increase of NDF and ADF concentration and linear decrease of IVDMD and CP concentration in extrusa from day one to day four during the grazing period. Values of intake were greater for mombaçagrass. There was no difference regarding the BW gain of steers between forages or irrigation levels.
animal performance; chemical analysis; tropical forages
