|Support type:||Scholarships in Brazil - Scientific Initiation|
|Effective date (Start):||March 01, 2013|
|Effective date (End):||December 31, 2013|
|Field of knowledge:||Agronomical Sciences - Animal Husbandry - Animal Nutrition and Feeding|
|Principal Investigator:||Luis Felipe Prada e Silva|
|Grantee:||Renan Augusto Pinheiro Maciel|
|Home Institution:||Faculdade de Medicina Veterinária e Zootecnia (FMVZ). Universidade de São Paulo (USP). São Paulo , SP, Brazil|
The increasing demand for food generated by the steep growth of human population over the last decades has aroused interests in researches aiming to improve the efficiency of beef production. In this context, the study of Beta-adrenergic agonists, due to its possibility of increasing production and financial efficiency, could be highlighted. Beta-adrenergic agonists are organic molecules which bind to receptors present in most mammalian cells, whose main effects are hypertrophy of muscle-tissues, and decrease in fat deposition. Among the known Beta-adrenergic agonists, ractopamine stands out for having a clear effect in most species and for the safety of use. Thus, the aim of this research is to evaluate the effect of orally feeding ractopamine to beef cattle during the finishing phase on the following parameters: growth performance, feed efficiency, carcass characteristics, development of muscle tissue and fat, protein and energy metabolism. Forty eight Nellore bulls will be used with approximately 360 kg of initial weight and 24 months of age. The animals will be housed for 100 days, being 21 days of adaptation and 79 of experimental period. The diet will consist of a roughage:concentrate ratio of 30:70 with Cynodon spp hay as the roughage and a corn, soybean meal-based concentrate. The experiment design will be of random blocks (initial weight) with the 48 animals divided into 16 pens. The treatments will be randomly allocated to pens within each block, in a 2x2 factorial arrangement of treatments. Treatments will be two doses of ractopamine (0 and 300 mg/d) and two levels of dietary protein, 100 or 120% of the estimated metabolizable protein requirement. Animal performance will be determined through periodic weightings of the animals, intake will be measured daily, blood samples will be collected for assessment of protein and energy metabolism. At the end of the treatments all the steers will be weighted and slaughtered. In the abattoir the carcass hot weight and carcass yield will be evaluated.