| This experiment was conducted to investigate the effects of tea polyphenols(TP) supplemention to diet of laying hens during whole egg-laying period on the cholesterol content in eggs,we expected that this study could accumulate more data for producing fresh eggs with low cholesterol content.Firstly,we determined the appropriate dosage of tea polyphenols through dose response.Then,we investigate the effects of tea polyphenols(TP) supplemention to diet of laying hens during whole egg-laying period on the cholesterol content in eggs.Finally,the mechanism of lowering cholesterol by tea polyphenols was explored through biochemical indexes and gene expression related to cholesterol metabolism.This study is divided into the following three experiments:Test 1.A total of 1800 of 48-week old Roman commercial laying hens were randomly divided into 6 groups with 6 replicates and 50 birds per replicate.The control group fed basal diet,and the experimental group fed basal diet supplemented with 150,200,250,300 and 350 mg/kg of tea polyphenols.1 week pro-feeding period is designed before 3 weeks experimental period.The result showed: compared with the control group,diet supplemented with 300mg/kg TP had no significant effect on the intake,laying rate,egg weight and the ratio of feed to egg(P>0.05).Compared with the control group,diet supplemented with 300 mg/kg TP had no significant effect on eggshell strength,eggshell thickness,the proportion of the yolk,yolk color and Haugh unit(P>0.05).The cholesterol content of yolk(mg/yolk)decreased with the increase of the concentration of tea polyphenols,compared with control group,the cholesterol content of yolk in the 300 mg/kg group decreased by 18%(P<0.05).Compared with the control group,the serum TC and TG contents in the 300mg/kg group were significantly reduced(0.01<P<0.05),and LDL-C were very significantly reduced(P<0.01).In the range of 150 mg /kg to 300 mg/kg,the above indexes decreased with the increase of tea polyphenols,and showed an opposite trend at 350 mg/kg.Compared with the control group,serum GSH-Px activity increased significantly with the increase of tea polyphenols(P<0.01),and was the highest in the 300 mg/kg group.Serum MDA content was significantly decreased with the increase of tea polyphenols(P<0.01),and was lowest in the 300 mg/kg group.In conclusion,the dietary addition of 300 mg/kg tea polyphenols has no significant effect on the production performance of laying hens,and can reduce the cholesterol content of egg yolk and improve the antioxidant capacity of laying hens.Test 2.300 mg/kg tea polyphenols were added into the diet of laying hens during the whole egg-laying period from 24 to 72 weeks to investigate the effect of tea polyphenols on the production performance and the cholesterol content of egg yolk.600 Roman commercial laying hens were randomly divided into control group and TP group,each group with 6 replicates and 50 birds per replicate.The basic diet with or without 300mg/kg TP was given to the experimental group and the control group during the period from 24 to 72 weeks of age.Production performance,egg quality and cholesterol content in eggs of laying hens was observed at the early(28 weeks old),middle(38,48 weeks old) and late(58,68 weeks old) egg-laying stages.The results showed that the addition of 300mg/kg tea polyphenols to the diet had no negative effects on the lying rate,egg weight and feed-egg ratio of laying hens in the whole egg-laying cycle.Compared with the control group,the laying rate in the TP group was significantly increased at 38 weeks of age(0.01<P<0.05),the ratio of feed to egg was significantly reduced(0.01<P<0.05),and the egg weight was significantly increased at 58 weeks of age(0.01<P<0.05).Dietary supplementation with 300 mg/kg tea polyphenols had no negative effect on egg quality at the whole egg-laying period.Compared with the control group,the eggshell strength and the eggshell thickness of the TP group were significantly increased at 38 weeks of age(0.01<P<0.05),and the haugh unit was increased at 28 week of age(0.01<P<0.05).Compared with the control group,the yolk cholesterol content of the control group was significantly reduced at each week-old point(0.01<P<0.05).After 38 weeks of age,the decline was stable at about 20%.In conclusion,dietary supplementation of 300 mg/kg tea polyphenols has no negative effects on the production performance and egg quality of laying hens at during the whole egg-laying period,but can steadily reduce the cholesterol content of egg yolk in middle and late egg production of laying hens.Test 3.1 healthy birds in Test 2,at 68 week of age and with body weight at 2.15±0.05 kg,were respectively selected from each repeat of control and TP group.Blood serum was collected wing vein for determination of lipid character,antioxidant capacity,serum hormone content.Live and ovary were collected after slaughter to determined lipid character,antioxidant capacity and genes related to lipid metabolism as well.The results showed: Compared with the control group,dietary supplementation of 300 mg/kg tea polyphenols can significantly reduce TG and TBA levels in laying hens' liver(0.01<P<0.05).HE staining and oil red O staining showed that tea polyphenols could improve hepatic steatosis and reduce hepatic fat deposition in laying hens.Compared with the control group,dietary supplementation of 300 mg/kg tea polyphenols can significantly reduce plasma TG and TC levels(0.01<P<0.05),and extremely significantly reduce plasma LDL-C level by 25.32%(P<0.01).But there was no significant effect on plasma TBA,HDL-C and LDL-C/HDL-C ratio(P>0.05).Dietary supplementation with 300 mg/kg tea polyphenols significantly reduced plasma insulin,estradiol and progesterone levels(P<0.01).No significant effect on ovarian TG and TC content(P>0.05).Compared with the control group,dietary supplementation with 300 mg/kg tea polyphenols significantly increased the activity of SOD enzyme and GSH-Px enzyme in liver and ovary(0.01<P<0.05),significantly increased the activity of GSH-Px enzyme in plasma(P<0.01),and significantly decreased the content of MDA in plasma(0.01<P<0.05).Compared with the control group,dietary supplementation with 300 mg/kg tea polyphenols significantly increased the expression of liver PPAR?,LXR?,and srebp-2(0.01<P<0.05),which are related nuclear receptors and nuclear transcription factors regulating lipid metabolism.In conclusion,the effect of tea polyphenols on lowering cholesterol in egg yolk is closely related to the plasma levels of TC and LDL-C,the insulin and the nuclear receptor-mediated signaling pathway may play an important role.In summary,the results of this study showed that dietary supplementation of 300mg/kg tea polyphenols had no negative effects effect on the production performance and egg quality of laying hens during the whole egg production period,and could steadily reduce the cholesterol content of egg yolk by about 20%.The effect of tea polyphenols on lowering egg cholesterol is closely related to plasma TC and LDL-C.Tea polyphenols reduce plasma cholesterol by lowering plasma insulin level and regulating the expression of nuclear receptors related to cholesterol metabolism in the liver,thereby affecting the acquisition of cholesterol by egg cells from plasma and reducing the deposition of cholesterol in egg yolk. |
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