The use of diets with high levels of concentrates is a common practice of feeding management for finishing animals needed to make the most of compensatory growth without harming the health of animals. Nevertheless, the high cost of power in this system requires the adoption of new technologies to remain competitive in the market. Apart from the possible metabolic consequences of diets with high content of non-fiber carbohydrates such as ruminal acidosis and reduction of productive life of the animals, as well as the economic viability still be questionable, especially in countries with favorable conditions for the use of pastures, as Brazil. In this context, the additives are used as in vitro rumen fermentation through the selection of gram-negative bacteria, which favors lower incidence of metabolic disorders and helps in animal performance. In Brazil, as over 72% of animals are confined or Nellore zebu and due to insufficient information in the literature on the energy value of forage used in the diet of Zebu, the objective of this study is to establish an appropriate minimum level of NDF from forage (NDF) in diets for finishing Bos taurus indicus, with monensin or functional oil as an alternative additive and evaluate the ingestive behavior, digestibility, ruminal fermentation, animal performance, carcass characteristics and enteric methane emission, minimizing energy losses in the form of methane, thus increasing the sustainability of the beef production chain through animal nutrition. For this, 70 Nellore male, unneutered, will be allotted to a randomized complete block in a 3x2+1 factorial arrangement, using two additives (Functional Oil Essential ® and monensin) and three levels of NDF (6, 9 and 15% DM ) using brachiaria hay as forage. To measure daily production of methane gas will be used methodology of SF6 tracer gas, the rumen daily monitoring (pH and temperature) will be done through rumen sensor (bolus) and feeding behavior through sensors supply. The animals will be slaughtered at the end of the experiment once they reach the slaughter weight determined (500 kg), for further analysis of carcass, meat and gastrointestinal tract.
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