Growth performance and safety of meat from cattle feedlot finished with monensin in the ration

Monensin is an ionophore antibiotic, the inclusion of which in the feed of beef cattle favors the best use of feed nutrients, via ruminal modulation. However, there are concerns regarding the residence of residues in the carcass from metabolism of monensin. The objective of this study was to evaluate the productive performance, carcass characteristics, serum parameters, tissue residual depletion and economic benefit of finishing of young bulls in confinement with monensin in the ration. Thirty-six animals were confined, and given 50% corn silage feed and 50% more concentrated feed. The experimental design was completely randomized, with two treatments (with or without monensin) and 10 replicates for the control group and eight for the monensin group. The use of monensin reduced the dry matter intake in relation to live weight (2.36% vs 2.55%), and improved feed conversion (8.61 vs 10.06 kg kg?1); the animals presented higher live weight (511 vs 494 kg), higher warm carcass weight (285 vs 272 kg) and an increase in fat thickness (4.97 vs 4.25 mm) compared to control animals. These increases in performance gave higher economic results, with a profit margin of R$ 122.84 per animal. A waiting period of 16 h before slaughter resulted in monensin concentrations below 0.25 µg kg?1 in edible organs and tissues, values well below those permitted by legislation. The use of monensin for young bulls in confinement promoted improvements in productive and economic performance, without leaving residues in edible tissues.