Effect of Tea Polyphenol on Serum Hormone, Serum Enzyme Activity and Antioxidant-Related Gene Expression in Chinese Yellow Chicken under Heat Stress

The present study was conducted to evaluate the effects of dietary supplementation of tea polyphenol （TP） on serum hormone, serum enzyme activity, antioxidant-related and immune-related gene expression of laying hens under heat stress. A total of 288 Chinese yellow chicken (186 days old) were randomly distributed among two treatments, each of which included 6 replicates of 24 hens. Dietary treatments were that the basal diet was supplemented with 200 mg / kg tea polyphenol. The study lasted for 7 weeks, including 1 week of adaptation and 6 weeks of the formal test. The content of high-density lipoprotein cholesterol (HDL-C) and total protein (TP) in serum significantly decreased by dietary supplementation with tea polyphenol. Dietary tea polyphenol supplementation improved serum superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) enzyme activity and decreased serum malondialdehyde (MDA) content in treatments compared to the control. However, supplementation of tea polyphenol did not affect the activity of serum catalase (CAT). The results indicated that long-term feeding of tea polyphenols help to increase the amount of hormones (FSH, E2) associated with reproduction in laying hens and thus improve egg production. It also improved the immune function of laying hens in high temperature environments. Adding tea polyphenols to the diet can significantly increase the serum IgG, IgM content of the laying hens and can upregulate the IgA content. Dietary supplementation of tea polyphenols in the laying hens significantly increased the expression of antioxidant enzyme-related genes (SOD, CAT and GPX1) in the liver. Moreover, the addition of tea polyphenols significantly increased the expression of immune-related genes (Interferon-γ (INF-γ), Interleukin 2 (IL-2) and Interleukin 4 (IL-4)) in the spleen. It is concluded that addition of tea polyphenols has a positive effect on antioxidant activity and immune function of laying hens.