The objective was to evaluate the performance of steers with different diet alternatives containing the r-zeta® additive (Zorion US LLC). A total of 54 Hereford steers (335.8 kg LW) were assigned to three treatments (two repetitions/treatments): 1) control: adaptation ration with a corn-based diet with protein concentrate (PC; 45% crude protein) and salt for intake control (78:15:7 ratio); 2) corn + PCt: self-feeder with whole corn grain and r-zeta® protein concentrate (80:20 ratio); and 3) PB _r-zeta®: self-feeder with pelletized balanced feed with the additive. The r-zeta® composition consists of flavorings for regulate intake, products that minimize thermal stress, enzymes, microorganisms that modulate the microbiota, liver protectors, and anti-inflammatories. Diets were formulated to be isonitrogenous and isoenergetic and were offered in self-feeders. The ADG, TKG, intake, and conversion were estimated. Indicators associated with thermal comfort were observed. The experiment ended at 70 days when the animals reached 430 kg LW and were sent to slaughter to estimate the carcass yield. In all groups, the ADG was similar (1.2 to 1.4 kg/animal/d). The intake in the control was higher (10.8 vs. 7.8 kg DM/animal/d); therefore, the conversion was also higher (8.0 vs. 5.1 to 6.0 kg DM/kg LW) compared to the groups with the additive. The control group presented a higher rate of respiration per minute compared to the corn + r-zeta® CP treatment (91 vs. 78 rpm) and also a higher frequency of panting. Carcass yield was similar between groups (58.5%; p= 0.7188). In conclusion, animals can be fattened without adaptation protocols. The performance and thermal comfort improve with additive inclusion in finishing diets.