RESUMO. O objetivo deste estudo foi avaliar o efeito de diferentes doses de nitrogênio em pastos de Urochloa brizantha cv. Marandu diferidos, e suas implicações sobre a viabilidade econômica da produção de novilhas da raça Nelore. Utilizou-se o delineamento inteiramente ao acaso, com quatro tratamentos (T1 = pasto diferido sem adubação nitrogenada; T2 = pasto diferido com 50 kg de N ha-1; T3 = pasto diferido com 100 kg de N ha-1; T4 = pasto diferido com 150 kg de N ha-1) e quatro repetições (16 piquetes adubados). Foram utilizadas, inicialmente, 48 novilhas da raça Nelore, com média de oito meses de idade e com peso corporal inicial de 178,69 ± 26,67 kg, sendo distribuídas três novilhas por piquete em todos os tratamentos em um sistema de pastejo sob lotação contínua, com taxa de lotação variável. Apenas o tratamento sem adubação nitrogenada apresentou valores monetários negativos de R$ -181,96; R$ ha-1 -72,79 e R$ @-1 -32,11. No entanto, o tratamento com 50 kg de N ha-1 apresentou os maiores valores monetários positivos com R$ 756,02; R$ ha-1 302,40 e R$ @-1 50,52. Os dados da viabilidade econômica na produção de novilhas de corte demonstram que o tratamento com 50 kg de N ha-1 é o mais viável financeiramente, nas condições de realização desta pesquisa.

ABSTRACT. The objective of this study was to evaluate the effect of different levels of nitrogen on deferred pastures of Urochloa brizantha cv. Marandu, and the implications on the economic viability of production of Nellore heifers. This was a completely randomized design with four treatments (T1 = deferred pasture without nitrogen fertilization; T2 = deferred pasture fertilized with 50 kg N ha-1, T3 = deferred pasture with 100 kg N ha-1, T4 = deferred pasture with 150 kg N ha-1) and four replications (16 fertilized paddocks). First, there were used 48 Nellore heifers, average eight months of age and initial body weight of 178.69 ± 26.67 kg, with three heifers in each paddock, in all treatments, in a continuous grazing system, with variable stocking rate. Only the treatment the without nitrogen fertilization showed negative monetary values of R$ -181.96, R$ ha-1 -72.79 and R$ @-1 -32.11. The treatment with 50 kg N ha-1 achieved the highest positive monetary values of R$ 756.02, R$ ha-1 302.40 and R$ @-1 50.52. Economic viability data in beef heifer production demonstrate that the treatment with 50 kg N ha-1 is the most financially viable under the conditions of this study.

The effects of the addition of saltbush on the fermentation characteristics and nutritional value of silages of elephant grass (Pennistum purpureum Schum.) were studied through a completely randomized design with six old man saltbush (Atriplex nummularia Lind) levels (0, 20, 40, 60, 80 and 100 %) in substitution of the grass natural matter, with six replicates. Elephant grass presented 18.9% dry matter (DM) and silages were produced in experimental PVC silos, which were open at 70 days after ensilage. The increasing old man saltbush levels had increasing linear effect on the DM content of silages. There was quadratic effect for the contents of lactic and acetic acids and in vitro DM digestibility. Contents of butyric acid were negligible. Values pH of and N-NH3 contents had increasing linear effect. Linear effect of the increasing levels of old man saltbush was verified on the CP contents. Neutral detergent fiber, total carbohydrates and ether extract were not affected, whilst acid detergent fiber content showed decreasing linear effect. The addition of old man saltbush in the ensilage of elephant grass favored the fermentation process, promoting good lactic acid contents and reducing acetic acid, pH, dry matter loss and ammoniacal nitrogen, in addition to improving the nutritional quality of the elephant grass silages.

O experimento avaliou o coeficiente de digestibilidade aparente (CDA) da matéria seca (MS), energia bruta (EB), extrato etéreo (EE) e proteína bruta (PB) de ingredientes do Semi-Árido Nordestino: farinhas do feno de maniçoba (FM), do feno de leucena (FL) e do feno da folha de mandioca (FFM), raspa de mandioca (RM) e resíduos de vitivinícola (RV) para tilápia do Nilo (Oreochromis niloticus). Os CDA para a MS, EB, EE e PB foram de 20,74%, 30,30%, 48,36% e 71,72% para FL; 19,34%, 17,08%, 30,03% e 44,88% para FM; 30,32%, 23,04%, 4,43% e 21,07% para FFM; 72,85%, 70,62%, 81,78% e 84,51% para RM e de 33,38%, 50,80%, 79,39% e 67,25% para RV. O feno de leucena, a raspa de mandioca e os resíduos de vitivinícola são promissores para a formulação de rações. A utilização dos ingredientes testados na composição de rações artesanais ou comercias para a tilápia do Nilo, bem como os níveis seguros para a inclusão destes devem ser testados.

The experiment evaluated the apparent digestibility coefficient (CDA) of dry matter (DM), gross energy (GE), ether extract (EE) and crude protein (CP) of regional alternative ingredients of Semi-arid Northeast as flour of maniçoba hay (FM), of Leucaena hay (FL) and of cassava leaves (FFM), as well as cassava scrapings (RM) and residues of wine (RV) for Nile tilapia (Oreochromis niloticus). CDA for DM, GE, EE and CP were 20.74%, 30.30%, 48.36% and 71.72% for FL, 19.34%, 17.08%, 30.03% and 44.88% for FM, 30.32%, 23.04%, 4.43% and 21.07% for FFM, 72.85%, 70.62%, 81.78% and 84.51% for RM and 33.38%, 50.80%, 79.39% and 67.25% for RV. The leucaena hay, the cassava scrapings and residues of wine are promising for the formulation of diets for Nile tilapia. However, the use of tested ingredients in commercial and homemade diets to Nile tilapia, as well as the safe inclusion levels of these should be tested.