Dominguez P.A., Pro-Martinez, A., Narciso-Gaytán, C., Hernández-Cázares, A., Sosa-Montes, E., Perez-Hernandez, P., Caldwell, D. and Ruiz-Feria, C. A. 2015. Concurrent supplementation of arginine and antioxidant vitamins E and C reduces oxidative stress in broiler chickens after a challenge with Eimeria spp. Can. J. Anim. Sci. 95: 143-153. Oxidation is a major problem associated with pathogen damage in animals. One-day-old mixed-sex broiler chicks (Cobb 500; n=624) were randomly assigned to one of six treatments: a basal diet [CTL; 40 mg of vitamin E (VE) kg^-1 of feed and 1.5% Arginine (Arg)] or the basal diet plus Arg (ARG; 0.3%), Arg VE (AVE; 0.3% and 40 mg kg^-1 respectively), Arg vitamin C (VC) (AVC; 0.3% and 1 g kg^-1 respectively), VE VC (VEC; 40 mg 1 g kg^-1 respectively), or Arg VE VC (AVEC; 0.3% 40 mg 1 g kg^-1 respectively). At day 14, all birds were orally challenged with 100× the normal dose of Advent^® coccidiosis vaccine (450 000 oocysts). Intestinal lesion scores (LS) in duodenum, jejunum and ceca were recorded, along with relative immune system organ weights at day 23. Plasma samples were taken before (2 h) and after challenge (12, 24 and 48 h) to determine malondialdehyde (MDA), nitric oxide (NO) and glutathione peroxidase activity (GPx). Birds fed the VEC diet were heavier at 7 d (P<0.05) than birds fed the AVE diet. CTL birds had heavier (P<0.05) bursas than AVC birds; no differences among treatments for spleen and thymus were found. The jejunum LS was lower in the AVC and VEC birds than in CTL birds, whereas ceca LS was highest in AVE birds, and the duodenum LS was not affected by treatment. Birds fed the AVEC diet had the lowest MDA levels before challenge, but higher levels of MDA than birds fed the CTL, ARG or AVE 12 h after challenge. Before challenge ARG birds had higher (P<0.05) NO levels than AVEC-fed birds, but 12 h after challenge birds fed the CTL, ARG or AVE diet had lower NO levels than birds fed the AVC, VEC or AVEC diet. Before challenge AVEC-fed birds had higher (P<0.001) GPx activity than CTL, ARG and AVE birds, but after 12, 24 and 48 h VEC birds showed higher GPx activity than CTL, ARG- and AVE-fed birds. Although Arg, VE and VC, modulated oxidative stress during coccidiosis challenge, the effects were not sufficient to affect performance relative to the control diet.