Based on the observations of this study, the addition of different GTB levels had an effect on some tested parameters. Growth performances were negatively and carcass composition was positively, affected at higher GTB concentrations (2%). Carcass characters, meat quality and hematological parameters did not consistently change with GTB concentration. Strong antioxidative activities were observed in the GTB groups. Our results also indicate that the addition of GTB to the diets of finishing pigs increases immune related cells, and enhances Il-6 and TNF-α production. Future studies are needed to elucidate the mechanisms for potentially enhanced immunity and to investigate its antimicrobial effect in challenged pigs