Research On Effect And Mechanism Of Tea Polyphenols On Production Performance,Egg Quality And Intestine Health Of Laying Hens In Vanadium Containing Diets

Vanadium is a heavy metal that can exert negative effect of laying hens' health and egg quality by causing oxidative stress. Tea polyphenols (TP) is a nature antioxidant, which may benefit layers under oxidative stress. Two experiments were conducted to determine the effect of tea polyphenols (TP) on production performance, egg quality, intestinal microflora and the mechanism of eggshell color change of laying hens in V containing diets. It provided a theoretical basis for feed and egg safety, which is important to the development of poultry industry.Experiment 1:The effect of tea polyphenols on production performance, egg quality, intestinal health of laying hens in vanadium containing diets.A total of 300 Lohman laying hens (67-wk-old) were used in a 1 plus 3×3 experiment design that hens were given either a diet without vanadium and TP supplementation (control) or diets supplemented with 5,10,15mg V/kg and TP (0, 600, 1000mg/kg) diets for 8 wks which included two phases,5 wks accumulation phase and 3 wks depletion phase.Results:Dietary vanadium addition decreased (linear, P<0.01) albumen height, Haugh unit (HU) and eggshell thickness, and eggshell redness (linear and quadratic, P<0.05) and yellowness (linear and quadratic, P<0.05) were decreased as vanadium levels increased. The eggshell bleaching effect were observed when dietary V supplementation more than 5mg/kg, and no difference were found between 10 and 15mg/kg groups. The 600 and 1000 mg/kg TP supplementation mitigated (linear effect, P<0.01) this reduction effect induced by vanadium during accumulation phase. In depletion phase, the bleaching effect on eggshell induced by vanadium disappeared 1-wk after vanadium withdrawal.. Eggshell thickness, eggshell strength, albumen height, HU were lower (P<0.05) in 15 mg/kg vanadium groups compared with control diet until 2-wk post vanadium challenge, but hens fed 15 mg/kg vanadium and 600 mg/kg TP groups shown no difference with control diet only after 1-wk withdrawal. In liver, the activity of glutathione S-transferases (GSH-ST) was decreased (linear. P<0.01)and glutathione peroxidase (GSH-Px) was increased (linear, P<0.01) with the TP addition at 5 wk in accumulation phase in vanadium-containing diet, the malondialdehyde contents has increased (linear effect, P=0.02) with the addition of vanadium in accumulation phase. Supplementation 15mg/kg V can significantly increase the crypt depth of the duodenum (P<0.01), and tend to decrease villous height to crypt depth ratio (P=0.06). Vanadium addition could significantly increase the apoptosis rate (P<0.01) of duodenal epithelial cells, with the 15mg/kg V treatment has the highest apoptosis rate. Supplementation TP could reduce the apoptosis of duodenal epithelial cells induced by V (P<0.01), and the 1000mg/kg TP exert better effect than 600mg/kg group. Fed 5mg/kg V to layers has a tendency to decrease the microbial diversity index (P=0.07), degree of homogeneity (P=0.07), and richness (P=0.06) in cecal., Addition of 1000mg/kg of TP in 10mg/kg V containing diet significantly reduced the cecal microbial diversity index, degree of homogeneity, and richness (P<0.01). Dietary supplementation of 10mg/kg of vanadium tend to increase the number of total bacteria in cecum (P=0.06), and TP did not influence cecal Escherichia coli, lactic acid bacteria, total bacteria proliferation. Compared with 5mg/kg vanadium,15mg/kg had a tendency to enhance acetic acid content (P=0.06) in cecal. Add 1000mg/kg TP in V containing diets can significantly improve cecal propionate (P=0.02) and butyric acid (P=0.02) content compared the groups without TP or with 600 mg/kg TP addition.Experiment 2:The effect and mechanism of tea polyphenols on eggshell color change of laying hens in V containing diets.A total of 90 Lohman laying hens (67-wk-old) were randomly divided into 3 groups with 6 replicates of 5 birds each for a 35-day feeding trial.. The dietary treatments were as follows:(1) control, fed a basal diet; (2) vanadium treatment, CON +10mg V/kg; (3) TP treatment:V10+600mg TP/kg.Results:In the uterus, the GST activity was reduced and the content of malondialdehyde (MDA) was increased in 10mg/kg V group compared to control group, whereas TP decrease the content of MDA, and increased GSH-ST enzyme activity (P<0.05). Adding 10mg/kg of vanadium in feed can increase the apoptosis rate of uterine epithelial cells, and 600mg/kg TP can alleviated the apoptosis rate induced by 10mg/kg V. Feed adding vanadium can significantly reduce the ferrochelatase (FECH), NF-E2-related factor 2 (Nrf2) mRNA expression and protoporphyrin IX content, tea polyphenols up-regulated the mRNA expression of Nrf2 but not FECH. Tea polyphenols supplemented at 600mg/kg can significantly improve the HO-1 mRNA expression, while 10mg/kg V treatment have no effect on heme oxygenase (HO-1) mRNA expression.In summary:supplementation of 10,15 mg/kg vanadium resulted in reduced albumen quality, bleaching effect on eggshell color, increasing apoptosis rate of duodenum epithelial cell, and accumulating in liver and uterus to causing oxidative stress, which may related to down-regulation of uterine Nrf2 and FECH mRNA expression and protoporphyrin IX content in uterus. The effect of TP addition can prevent laying hens from the adverse effect of vanadium on egg quality and shorten the recovery time. TP addition of 600mg/kg can significantly alleviate decreased antioxidant levels caused by V, decrease the apoptosis rate of uterine epithelial cells, altered microflora profile and SCFA content, increased the expression of Nrf2 and HO-1 mRNA.Therefore to protect the eggshell from bleaching effect induced by V.