Pozzo, L., Tarantola, M., Biasibetti, E., Capucchio, M. T., Pagella, M., Mellia, E., Bergagna, S., Gennero, M. S., Strazzullo, G. and Schiavone, A. 2013. Adverse effects in broiler chickens fed a high lycopene concentration supplemented diet. Can. J. Anim. Sci. 93: 231-241. The present investigation was designed to assess the effects of the administration of a high dietary lycopene dose to broiler chickens on growth and slaughter performances, haemato-biochemical parameters, antioxidant enzymes, histological lesions and lycopene accumulation in the tissues. Thirty-six 1-d-old male Hubbard broiler chicks were examined and divided randomly into two groups (three replicates for each dietary treatment): the Control group, which received a basal diet, and the Lycopene group, which received the basal diet supplemented with 500 mg lycopene kg^-1 diet. The experimental period lasted 35 d and growth performance was recorded on a weekly basis. At the end of the experiment (day 35), blood samples (n=12) were collected from the femoral vein. Erythrocyte and leukocyte numbers were assessed and the heterophil-to-lymphocyte ratio was determined. The alpha-1-acid glycoprotein, lysozyme, total protein and the electrophoretic patterns were evaluated in serum samples. Nine chickens per group were slaughtered to measure the carcass yields and the weight of the liver, spleen, bursa of Fabricius and thymus. Spleen, liver, and bursa of Fabricius samples were collected for histological examination and fixed in 10% neutral buffered formalin. The lycopene concentration, thiobarbituric acid reactive substances (TBARS) and chemical composition were assayed in breast meat and thigh samples. The TBARS, glutathione content, catalase and superoxide dismutase activity were measured in liver and kidney samples. The high lycopene concentration supplemented diet did not affect the birds' growth, slaughter performance or antioxidant enzymes in the breast meat, thigh meat, liver and kidney samples. The concentrations of lycopene in the breast and thigh of the lycopene-supplemented group were 0.10±0.05 mg kg^-1 and 0.42±0.35 mg kg^-1, respectively, while no lycopene was found in the Control group. Spleen and bursa of Fabricius of birds fed a diet supplemented with a high level of lycopene showed weight decrease (P<0.05) and degenerative lesions (P<0.05). Moreover, lycopene supplementation reduced the serum protein concentration, albumin, alpha and the gamma globulin serum concentration (P<0.05).