Effects Of Conjugated Linoleic Acid On Performance,Egg Quality,Fatty Acid Profile Of Egg Yolk And Cholesterol Metabolism In Primiparous Laying Hens

This study is to provide scientific evidence for the application of conjugated linoleic acid(CLA)in laying hens,and to explore the mechanism of CLA regulating cholesterol metabolism in laying hens.The entire research includes two experiments as followed:1.Effects of conjugated linoleic acid on the production performance,egg quality,yolk firmness and yolk fatty acid composition of primiparous laying hensSix hundred and thirty 18-week-old Hy-Line brown laying hens were divided randomly into 7 groups with 6 replicates per group and 15 birds in each replicate.The control diet had no CLA,and the experimental diets contained 1%,2%,3%?4%?5% and 6% CLA,respectively.The feed trail lasted for eight weeks followed an adaptation period of one week.The results showed as follows: 1)production performance,egg and eggshell quality were no significant difference when the diet CLA?2%(P>0.05).Compared with the control group,eggshell thickness was extremely significant increased in 2%,3% and 4% CLA groups(P<0.01),laying rate was significantly reduced and the yolk firmness was extremely significant increased when the diet CLA ?3%(P<0.01),feed intake was extremely significant reduced when the diet CLA?4%(P<0.01),the ratio of feed to egg was significantly increased and yolk to egg weight ratio was significantly reduced when the diet CLA?5%(P<0.05).2)Compared with the control group and other experimental groups,the content of C16:0,C18:0 and SFA in yolk were extremely significant reduced in 1% and 2% groups(P<0.01),but they were extremely significant increased when the diet CLA?4%(P<0.01).The content of C16:1,C18:1,MUFA and PUFA were extremely significant reduced in experimental groups(P<0.01).The content of CLA in egg yolk increased quadratically with the increase of CLA level in layer diets(P<0.01).The c9,t11-CLA isomer in egg yolk is 1.67 times the content of the t10,c12-CLA isomer in all treatments.It is concluded that dietary 2% CLA improve the quality of eggshell,decrease the content of SFAs in egg yolk and a certain amount of CLA can be enriched in egg yolk.2.Effects and gene regulatory mechanism of conjugated linoleic acid on cholesterol metabolism of laying hensA total of 360 eighteen-week-old Hy-Line brown laying hens were randomly divided into 4 groups with 6 replicates per group and 15 birds per replicate.The control diet had no CLA,and the experimental diets contained 1%,2% and 4% CLA,respectively.The feed trail lasted for eight weeks followed an adaptation period of one week.The results showed as follows: 1)the abdominal fat rate of laying hens in the 2% and 4% CLA groups was significantly lower than that in the control group(P<0.05),but there was no significant difference in body weight gain(P>0.05).The liver index in group 4% CLA was significantly higher than that in control group(P<0.05).2)On day 28 and day 56,the content of HDL-C in 2% CLA group was significantly higher than the control group(P<0.05),and the ratio of HDL-C/LDL-C in 2% CLA group was extremely significant higher than the control group(P<0.01).The content of LDL-C was significantly lower than the control group(P<0.05).But the serum TC and TG in treatment group and the control group had no significant difference(P>0.05).On day 56,the yolk cholesterol content in 2% and 4% CLA groups was significantly lower than the control group(P<0.05),and the egg cholesterol content in 2% and 4% CLA groups was extremely significant lower than the control group(P<0.01).The liver cholesterol content in 2% CLA group is significantly lower than the control group(P<0.05).3)Compared with the control group,the HMGR content in 2% and 4% CLA groups was significantly decreased(P<0.05),and mRNA expression was extremely significant decreased(P<0.01).The LDLR content in 2% and 4% CLA groups was significantly decreased(P<0.05),and mRNA expression was extremely significant decreased(P<0.01).The CYP7A1 content in liver was significantly lower than the control group(P<0.05).The expression of CYP7A1 mRNA in liver of laying hens in experimental groups were extremely significant lower than the control group(P<0.01).Our present study indicates that the diet supplemented with 2%CLA can improve the quality of eggshell and the metabolism of cholesterol in laying hens while the egg yolk can enrich with a certain amount of CLA.The possible mechanism of cholesterol lowering effects can result from reducing endogenous synthesis and promoting the transport of cholesterol in blood circulation.