Effects of different levels of green tea leaf powder on production performance and some blood parameters of laying hens

 Camellia sinensis is a species of evergreen shrub or small tree that its leaves is used to produce tea. The difference in the flavour, colour, and name of the tea depends on how the leaves are processed. There are four basic types of tea: black tea (tea leaves that are exposed to the air and allowed to fully oxidise or ferment, changing the leaves from green to black), oolong tea (it falls between black and green tea), green tea (less processed and not fermented), and white tea (the least processed of all tea). Green tea has over 200 bioactive compounds and contains over 300 different substances. The chemical composition of tea, composed of polyphenols such as catechins and flavonoids, alkaloids such as caffeine, theophylline, essencial oils and other compounds which are unknown (Carry et al. 2007). In most researches, green tea has beneficial effects due to the presence of catechins as powerful antioxidants. Ariana et al. (2011) reported that adding 1.5% green tea leaf to laying hens diet caused a decrease in feed intake compared with control diet. Bing et al. (2018) reported that up to 1% green tea leaf did not affect production performance, but levels above 1% reduced laying percentage. Some sources even reported better performance for the birds fed even lower levels of green tea. Abdul Azim (2005) reported that adding 0.75% of green tea improved the laying yield and feed conversion rate of Japanese quail. Due to complex compounds such as catechins, flavonoids and phenolic acids, antioxidant and cholesterol lowering effects of tea have been proved. Ariana et al. (2011) reported the reduction of serum cholesterol of laying hens fed 1.5% green tea leaf and Zeinab et al. (2010) showed an improvement in antioxidant capacity of birds fed green tea leaves. Due to lack of research on the effects of Iranian tea on laying hen performance and extensive cultivation of this product in Iran, this study was conducted to evaluate the effects of different levels of green tea on production performance, serum lipids, and antioxidant capacity of laying hens.

 One hundred and twenty W-36 white leghorn laying hens (60 wk age) were assigned to five treatments with five replicates and four birds in each replicate based on a completely randomized design. Dried Iranian green tea leaf provided from Lahijan city tea farms. Dietary treatments including: 1) Basal diet based on a corn-soybean meal 2) basal diet with 0.5 % green leaf tea powder, 3) basal diet with 1% green leaf tea powder, 4) basal diet with 1.5% green leaf tea powder, and 5) basal diet with 500 g/ton vitamin E. All of the diets were fed to birds for seven weeks. The diets were isocaloric and isonitrogenous. Egg production rate, egg weight, feed consumption, egg mass, and feed conversion ratio were recorded weekly and reported as hen day basis. Egg mass was calculated by multiplying the total number of eggs laid per hen by the average egg weight. At the end of the experiment, two birds from each replicate (close to cage average weight) were selected. Blood samples were collected from the wing and serum was separated. Total antioxidant capacity (TAC), lipid peroxidation (MDA), total cholesterol, triglyceride, and high-density lipoprotein (HDL) were measured using analytical kits. All data were analyzed by ANOVA procedure described by the SAS Institute (2009). Tukey test was used to determine the significant differences between treatment means.

 The results showed that feed intake, egg production rate, and egg mass of birds fed diets containing more than 0.5% green tea leaf powder (GTLP) decreased significantly and feed conversion ratio increased as compared with control group. Production performance criteria was not affected in birds fed vitamin E as compared with control group. Similarly, Bing et al. (2018) showed that feeding up to 1% of GTLP in layer hen diets did not affect production performance; but, levels above 1% reduced egg production percentage. Also, Bing et al. (2018) showed that the use of higher than 1% GTLP in diet had negative effects on production performance. Kojima and Yoshida (2008) and Wei et al. (2012), similar to our results, reported a decrease in feed intake even at lower levels of GTLP in the diet. Yaman et al. (1999) showed that egg weight decreased using 0.67% green tea extract in drinking water. As compared with control group, birds fed diet containing 1.5% GTLP had lower serum triglyceride, total cholesterol, and VLDL concentrations. Similarly, Ariana et al. (2011) reported a reduction in serum cholesterol of laying hens fed 1.5% GLTP. Shishikoura et al. (2006) reported that catechins in green tea is a potent inhibitor for cholesterol and triglyceride absorption in small intestine. Panala et al. (1997) showed that green tea polyphenols can reduce the production of free radicals produced in the cell and Ishikawa et al. (1997) reported that green tea flavonoids could be able to boost animal antioxidant capacity. Sahin et al. (2010) reported a decrease in malonildialdehyde (MDA) by feeding GLTP in birds. In the present experiment, serum antioxidant capacity was increased, but   MDA   and lipid peroxidation index were decreased in the birds fed diets having 1.5% GTLP or   vitamin E (P<0.05).

Although the use of at least 1% GTLP had negative effect on production performance of laying hens, it reduced blood cholesterol and triglycerides, while increased antioxidant capacity parallel to vitamin E diet.