Effects of dietary n-6:n-3 polyunsaturated fatty acid ratio on cardiac antioxidative status, T-cell and cytokine mRNA expression in the thymus, and blood T lymphocyte subsets of broilers

This study was conducted to assess the effect of modifying the n-6:n-3 polyunsaturated fatty acid ratio (FAR) of diet using linseed, soybean, and corn oil on growth performance, cardiac antioxidant status, T-cell and cytokine mRNA expression in the thymus, and blood T lymphocyte subset characteristics in broilers. A total of 480 one-day-old male broilers (BW=46±4 g) were randomly allotted into 4 treatments consisting of dietary n-6 to n-3 FAR of 12:1, 9:1, 6:1, and 3:1. There were 6 replicates per treatment with 20 birds per replicate. After feeding for 42 d, chicks were slaughtered, and the blood and tissue samples were collected. Decreasing n-6 to n-3 FAR did not affect feed intake, but increased BW gain (linear, P=0.05) and improved feed conversion ratio (quadratic, P=0.03) during the first 3 weeks. Cardiac hydroxyl radical (P=0.03) and malondialdehyde (MDA) (P=0.01) concentration reduced linearly with decreasing dietary n-6:n-3 FAR, whereas superoxide dismutase (SOD) (quadratic, P=0.04), glutathione S-transferase (GSH-ST) (quadratic, P=0.02) and glutathione peroxidase (GSH-Px) (linear, P=0.05) levels were increased. The T lymphocyte subsets were also analyzed using monoclonal antibodies and flow cytometry simultaneously. The messenger RNA (mRNA) expression of cluster of differentiation antigens (CD)4+ receptor and toll-like receptor (TLR)-3 in thymus were depressed (quadratic, P<0.05) by decreasing n-6:n-3 FAR, whereas the expression of interferon (IFN)-α was unaffected by dietary treatment. Concentration of blood CD4+, CD8+ and CD4+:CD8+ ratio linearly declined (P<0.05) as the n-6:n-3 FAR decreased. In conclusion, the decreasing n-6:n-3 FAR can enhance the levels of cardiac antioxidant enzymes, and affect thymus immune function of fast growing broilers.