Gene expression of enzymes and the profile of ruminal and intestinal microorganisms with health reflexes of dairy calves supplemented or not with oregano extract

The growing concern with the presence of traces of contaminants in animal products, which added to the bacterial resistance to conventional antibiotics, has stimulated the search for alternatives to chemical agents. Alternative additives, such as essential oils, have the potential to decrease the use of antibiotics without reducing performance or increasing mortality of dairy calves, modulating ruminal fermentation, control of microorganisms present in the gut, and improving overall animal performance. However, the results are mostly the result of studies with adult or in vitro animals, and there is a lack of knowledge about essential oils in calf feeding. The study will be composed of an experiment with the evaluation of the ruminal and intestinal microbioma, gene expression of ruminal development enzymes, histological parameters of the gastrointestinal tract and performance of calves supplemented or not with oregano extract. It will be used 16 male calves, with three to seven days of life, randomly distributed in a completely randomized design, with 8 calves per treatment. The animals will be housed individually, allowing individual daily control of the consumption of the liquid and solid diets. The animals will be weaned at 53 days, when they will be euthanized for the collection of digesta and tissues. Every two weeks the animals will be weighed, as will body measurements and the amount of supplement will be adjusted. Nutrient digestibility and nitrogen balance will be analyzed. In the ruminal and intestinal digesta samples, the DNA will be extracted for analysis of the total microbiota. Fermentation final products will also be determined. In the tissue samples, the development of ruminal papillae and intestinal villi will be analyzed. In the samples of rumen tissue will be isolated the RNA to determine the gene expression of the ketogenic enzymes.