Ninety Holstein bulls were used in a complete randomized design to study the effect of a blend of plant extract (PE) supplementation on jejunum, cecum, and rectum microbiota (Escherichia coli and lactic acid bacteria [LAB]) and hide and carcass contamination (identification of E. coli O157:H7 and Salmonella). Three treatments - control (CTR), monensin (MON), and PE - were tested. Bulls were offered straw and concentrate ad libitum during 108 d. In the cecum, the percentage of LAB counts below 5 log CFU/ml was greater (P < 0.01) in MON (68.1%) than in CTR (34.6%) and PE (28.0%) treatments. On hide, Salmonella was detected (P < 0.05) in CTR (13.3%) and MON (10.0%) treatments, in contrast to PE (0%) treatment. In bulls fed high-concentrate diets supplemented with PE, no increase of carcass E. coli O157:H7 and Salmonella identification was observed. Copyright ©, International Association for Food Protection.