Beef cattle feedlot is a strategy to increase the productivity, and to offer a great feedstock for the consumers. Ionophore and non-ionophore antibiotics have been used as feed additives for enable to supply of the high concentrate diets. The objective of this study was to evaluate the isolated and combined effects of the virginiamycin (VM) and monensin sodium (MON) in diets of crossbreed bulls feedlot. The animals were kept in feedlot in group pens for 105-d with a 28-d adaptation period. Three hundred thirty-nine 1/2 Nellore × 1/2 Guzera beef steers (402.7 ± 1.3 kg of initial BW) were used in a randomized complete block design with 5 treatments and 7 replicates (pens). The blocks were defined by initial BW. The treatments are defined by levels of the VM and MON (mg/kg of dry matter) as follows: 30MON; 15VM+30MON; 25VM+30MON; 34VM+30MON and 34VM. Animals were fed ad libitum twice daily with isonitrogenous and isoenergetic diets, with 88:12 concentrate: roughage (sugarcane bagasse) ratio. Bulls were weighted at the beginning, after the adaptation period and at the end of the trial. Nine animals were slaughtered at the beginning of the trial to determine initial hot carcass weight (HCW). At the end of the experiment, 330 bulls were slaughtered and determined the final HCW (Table 1). There was not statistical difference (P > 0.05) between the treatments for all variables studied. Therefore, the use of additives, MON and VM, isolated and combined, do not influenced the carcass characteristics. Table 1. Carcass data of the feedlot bulls fed with virginiamycin (VM) and monensin sodium (MON) in high concentrate diets

Variables	Additive (mg/kg DM)					SEM	Contrast (P-value)
MON 30				VM	VM vs. MON	L	Q	VM vs. VM/ MON
0	15	25	34	34
ICW (kg)	215	215	215	215	216	0.653	0.3142	0.2334	0.2706	0.2620
FCW(kg)	322	317	318	320	320	8.785	0.6798	0.7171	0.1076	0.9849
Dressing (%)	56.63	56.74	56.51	56.76	56.92	0.267	0.4125	0.8772	0.7957	0.6560
CG (kg)	106.33	102.43	102.18	105.07	104.07	3.701	0.5088	0.7079	0.1670	0.7695
BWG (kg)	166.56	159.02	160.36	162.88	159.53	5.500	0.1446	0.5162	0.1403	0.4795
GY (%)	64.04	65.63	64.19	64.53	65.38	1.203	0.4364	0.9963	0.6080	0.6206
ADCG (kg/d)	1.02	0.98	0.98	1.00	0.99	0.038	0.5029	0.7084	0.1706	0.7643