The objective of this study was to evaluate the performance and the quantitative characteristics of barrow's carcass maintained under thermoneutral environment and fed with diets containing different ractopamine levels. Forty-eight barrows were used, with initial weight of 67.0±2.7kg, distributed in a randomized blocks design with four ractopamine levels (0, 5, 10 and 20ppm) and six replicates with two animals each. The experimental period lasted 28 days. The average temperature recorded was 20.9±2.9°C, relative humidity was 86.7±7.3% and BGHI was 69.6±4.0. The final weight of the animals and feed intake were not influenced (P>0.05) by treatments. The ractopamine levels influenced (P<0.05) the daily weight gain and feed conversion. There was a linear reduction (P<0.05) of backfat thickness, increase of muscle depth and the carcass lean meat percentage in accordance with the increasing of ractopamine levels in the diet. The weight, carcass yield and loin eye area were not influenced (P>0.05) by treatments. It was concluded that the ractopamine optimal level of inclusion in the diet of barrows kept under thermoneutral environment is 20ppm.
additive; beta-agonist; carcass; performance
