This study aimed to evaluate the effects of the product Powerjet on the performance of lambs. This product is a patented combination of 3 plant extracts selected by their anti-inflammatory and antioxidant effects on the intestinal mucosa. The substances in these extracts, sanguinarine and honokiol and its isomer magnolol, also have an antioxidant effect inhibiting mitochondrial peroxidation in the liver and heart. Therefore, this study was carried out to evaluate these extracts compared with selenium (Se) plus E vitamin, known antioxidants, in the performance of lambs fed a high-concentrate diet. Forty-eight male lambs, just weaned, with a mean initial weight and age of 20 ± 1.5 kg and 60 d, respectively, were kept in individual pens with plastic bunks for feed and water and fed a diet composed exclusively of whole corn (80%) and a protein pellet (20%). The treatments differed only in the inclusion or not of the additives: a control diet without additives (CTL), a diet with the plant extracts (PX), a diet with Se and E vitamin (ES), and a diet with both additives (PXES). The PX inclusion in the diet was calculated to supply 4 mg/kg LW, and the Se and E vitamin inclusion was 1.0 mg/kg DM and 100 UI/kg DM, respectively. The CTL, PX, ES, and PXES diets had Se concentrations of 0.05, 0.05, 0.24, and 0.23 mg/kg DM, respectively. The Se requirement reported in the literature was between 0.10 and 0.20 mg/kg DM. The experimental design was random blocks in a 2 × 2 factorial (with or without PX and ES) arrangement, and the data were analyzed with the MIXED model of SAS 9.3 with a 5% level significance. The inclusion of ES and PX in the diets resulted in greater final weight (P = 0.015 and P = 0.064, respectively) and greater weight gains (P = 0.045 and P = 0.060, respectively), but there was no interaction between the studied factors (P = 0.365). The final weight means with ES and PX were 44.6 and 44.1 kg, respectively, and without ES and PX were 41.0 and 41.4 kg, respectively. The daily weight gains were, in the same order, 0.390, 0.389, 0.352, and 0.353. There was no effect (P = 0.303) of the inclusion of ES or PX in the DMI (mean 3.35%) nor interaction of the additives (P = 0.296). There was no difference (P = 0.110) in the feed efficiency, with a mean of 0.270 kg/kg DMI. Considering the results, the PX had a positive effect on performance.