The objective of this study will be to evaluate the effects of essential oil or monensin on dry matter intake variation, net energy and rumen tissue histological variables of Nellore cattle. The treatments will be disposed as follows: Control (with no additives); Monensin (with 30 ppm of monensin), Essential Oil (with 500 ppm of essential oils) and Monensin + Essential Oil (30 ppm and 500 ppm respectively). It will be used 96 Nellore yearling bulls, with approximately 370 kg of body weight. Cattle will be blocked by weight, and randomly distributed in 24 pens, which will be considered the experimental unit. In the beginning of the trial and every 28 days all animals will be weighed and the dry matter intake will be measured every day so than dry matter intake variation and energy consumption will be evaluated. At harvest, a 1-cm2 fragment of each rumen will be collected from ventral sac for histological assessment. Morphometric measurements, such as papillae surface area, papillae height, papillae width, keratinized layer thickness, and mitotic index will be determined.
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