Abstract Objective: Turmeric (Curcuma Longa Linn) is a medicinal plant that contains curcumin. There is a growing interest in using curcumin powder (CP) as feed additives for antioxidative and antimicrobial properties to improve human health. This study was conducted to determine the appropriate levels of CP on blood parameters, immunity, and histology of jejunum in hens. Materials and Methods: A total of 200, 58-wk-old Hy-line hens were randomly distributed into 4 treatments (0%, 0.5%, 1.5%, and 2.5% CP or 0, 5, 15, and 25 g/kg feed, respectively) with 5 replicates (10 birds each) for 8 weeks using the completely randomized design. Blood samples were taken from 2 birds per replicate at weeks 61 and 65 to evaluate blood parameters. On weeks 63 and 65, two birds from each replicate received 0.5 ml SRBC (25%) injection in breast muscle and 7 days later, blood samples were collected to evaluate total Ig, IgG, and IgM titers in serum. Two hens were sacrificed at week 65 for the histological study of jejunum. Results: Curcumin reduced triglycerides at 1.5% and 2.5% and cholesterol and LDL at 2.5% (p<0.05). Improvement of total Ig and IgG titers after the 1st and 2nd injections were observed. Muscle thickness in jejunum increased (p<0.05) at 1.5% curcumin and the length and surface area of villus were enhanced as well. Conclusion: Our results demonstrate that curcumin can be used as an antioxidant at 1.5% and antilipidemic agent at 2.5% in diet.

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