Grape seed extract, high altitude, lipid peroxidation, vitamin E. ABSTRACTThe aim of this research was to evaluate the effect of partial substitution of vitamin E (VE) by grape seed extract (GSE) on glutathione peroxidase activity (GPxA), nitric oxide (NO) concentration and lipid peroxidation [malondialdehyde (MDA) concentration] in the plasma, lungs, heart and liver, and live performance of broilers raised at 2278 m of altitude. One-d-old Ross 308 male chickens (n = 420) were randomly distributed into three treatments: Control-AL (basal diet containing 40 IU of VE and fed ad libitum; AL), Control-FR (basal diet and feed restriction; FR) and GSE-AL [basal diet containing 10 mg of GSE (equivalent to 30 IU VE) plus 10 IU of VE and fed AL]. The data were analyzed using one-way analysis of variance. Glutathione peroxidase activity, and NO and MDA concentrations in the plasma were evaluated on d 46. On d 47, MDA was evaluated in the lungs, heart and liver. Live performance parameters were recorded weekly. There were no significant differences (p>0.05) in live performance and NO concentration among treatments. Birds from the GSE-AL treatment presented the lowest (p<0.05) GPxA, the highest (p<0.05) MDA concentration in the plasma, heart and liver, and intermediate MDA concentration in the lungs. Our results suggest that GSE may partially replace VE in broiler diets without impairment of live performance. However, further research is required to determine the optimal level of dietary GSE inclusion to reduce lipid peroxidation in the plasma, lungs, heart, and liver of broilers raised at 2278 m of altitude.