Substituição total do farelo de soja por ureia extrusada em suplementos para novilhos de corte

Abstract

Two experiments were carried out at Fazenda Escola da Famez - UFMS, between February and June 2018, with the objective of evaluating the effects of replacing true protein (soybean meal) with non-protein (extruded urea) of supplemented cattle during the period of waters and water-dry transition. The experimental area was fixed with 4 paddocks with Brachiaria brizantha Stapf cv. Marandu (2 paddocks per treatment) and supplements were composed of mineral core, corn and soybean meal or extruded urea and provided 0.45% of PC in the waters and 0.7% of PC in the transition between waters and drought. In experiment 1, four crossbred and cannulated bovines were used in the rumen, distributed in a 2x2 double Latin square. The treatment containing soybean meal showed higher consumption and greater range of N-NH3 concentration in the ruminal fluid (5-33 mg/dL in the rainy season and 7-30 mg/dL in the wet-dry transition period). Mean pH values in both treatments and periods remained above 6.2, considered as the minimum limit for adequate fiber fermentation. There was no effect (P>0.05) on total VFA concentration (mMol/L) for treatments. The replacement of extruded urea by soybean meal in the diet was able to provide good results for blood parameters, as none of the analyzes exceeded the reference levels. In experiment 2, 36 nelore and annellate steers were used, distributed in a completely randomized design. It determines forage mass and pasture structure, supplement consumption, chemical analyses, performance and costs. Forage mass suffered a reduction of 31.9% between February and June. In the composition of the pasture, the proportion of leaves was generally greater than that of stem (25%:21%). There was an effect (P<0.05) of intake sources on supplement consumption in both periods. There was an effect (P<0.05) of disease sources on final live weight (FLW), total weight gain (TWG), average daily gain (ADG) and arroba gain during the rainy season and there was no effect of disease sources on the FLW, TWG, ADG and arroba win in the dry-water transition. There was an effect (P<0.05) of intake sources on supplement cost (total and daily), cost per hectare and revenue (per animal and per hectare) in the waters. There was an effect (P<0.05) on supplement cost (total and daily) and cost per hectare in the wet-dry transition. Total replacement of true protein by extruded urea in the growing phase during the rainy season is not recommended. It is recommended to replace soybean meal with extruded urea (Amiréia-200S®) in the protein supplementation of beef steers on pastures only during the water-dry transition period, due to better ruminal and blood parameters and lower cost compared to the treatment of true protein.