| This study used laying hens to evaluate the effect of different levels and sources of DHA supplementation on performance,egg quality,redox status,serum parameters,egg yolk DHA deposition and the immune responses,with an aim to access the tolerance effect of DHA on laying hens.And this thesis was conducted to determine the optimal supplementation level of DHA in laying hens diets.This study consisted of three experiments.Experiment 1.Effect of Microalgae oil and Fish oil on yolk fatty acid composition and egg quality of laying hens.This experiment was conducted to investigate the effects of different level and sources of DHA from microalgae oil and fish oil on yolk fatty acid(FA)composition and egg quality(including storage period)of laying hens,with the aim to provide basis for the production of DHA enriched eggs.Six hundred and thirty Hy-Line Brown laying hens of 31-week-old with similar laying rate were randomly allotted into 7 groups with 6replicates per groups and 15 hens per replicate.The laying hens in the control group were fed a basal diets without adding exogenous DHA sources,and the other six groups were fed the basal diets supplemented with either microalgae oil(MO)or fish oil(FO)at three different doses(1.35,2.7 and 5.4 mg/g).The measured values of DHA content in diets were 1.1,2.4,4.1,1.1,2.7 and 4.5 mg/g,respectively.The feeding trial lasted for 12 weeks after 1 week of adaption.The results showed as follows: 1)At the end of the experimental period eggshell strength,eggshell thickness,egg shape index and haugh unit were not significantly different(P>0.05),the albumen height of 1.35 mg/g groups were significantly higher than 2.7 mg/g and 5.4mg/g groups at the end of 4th week(P<0.05).Compared with control groups,dietary DHA groups significantly increased yolk color at the end of 8th week(P<0.05).2)No differences were found for MDA from yolk among all treatments when stored for 28 d at 4?.The storage period resulted in linear increase of yolk MDA.3)The FO groups had a higher haugh unit than MO groups when stored for 14 d at 4?.The interaction of DHA sources and levels showed significant effect on albumen height(P<0.05);the albumen height was decreased as dietary fish oil was increased,and was initially increased and then decreased as increasing inclusion of MO.The yolk color was significantly affected by sources(P<0.05),yolks from FO were better than yolks from MO source when stored at 4? for 7d and 28 d.4)Compared with the control group,dietary DHA groups significantly increased DHA,PUFA and ?-3 PUFA at the end of 12 th week,and these items were significantly affected by sources(P<0.01),FO groups were higher than MO groups.The FO groups had a smaller ratio of ?-6 PUFA to ?-3 PUFA than the MO groups.The incorporation efficiency of DHA in eggs were significant decreased as increasing inclusion of either MO or FO.In conclusion,compared with MO,FO was more effective to enhance the DHA enrichment in egg yolk and the 1.35 mg/g treatments had the highest incorporation efficiency.Experiment 2.Effect of Microalgae oil and Fish oil on immune function of laying hens.This experiment was conducted to investigate the effects of different level of Fish oil and sources of DHA from microalgae oil and fish oil on humoral and cellular immune responses of laying hens.Six hundred and thirty Hy-Line Brown laying hens of 31-week-old with similar laying rate were randomly allotted into 7 groups with 6 replicates per groups and 15 hens per replicate.he laying hens in the control group were fed a basal diets without adding exogenous DHA sources,and the other six groups were fed the basal diets supplemented with either microalgae oil(MO)or fish oil(FO)at three different doses(1.35,2.7 and 5.4 mg/g).The measured values of DHA content in diets were 1.1,2.4,4.1,1.1,2.7 and 4.5 mg/g,respectively.The feeding trial lasted for 12 weeks after 1 week of adaption.The results showed as follows: 1)Dietary supplementation of DHA did not significantly affect the splenic index,thymus index and serum immunoglobulin A concentration(P>0.05).2)Compared with control groups,MO1.35?MO2.7?MO5.4 and FO1.35 group's H9 antibody titers were significantly increased at 7 days after immunized(P<0.05),no differences were found for H9 antibody titers at 14 and 28 days after immunized(P>0.05).Immunized time remarkably affected the H9 antibody titers,with a increase in H9 antibody titers content observed with immunized time.Compared with control groups,MO1.35?MO2.7?MO5.4 and FO1.35 were significant increased at 7 days after immunized(P<0.05),MO1.35?FO1.35 and FO2.7 were significant increased at 14 days after immunized(P<0.05),MO1.35?MO2.7?FO1.35 were significant increased at 28 days after immunized(P<0.05).3)Compared with the control group,dietary supplemented with 1.35 and 2.7mg/g DHA significantly increased the gene expression of IL-2,IL-10 and IFN-?(P<0.05),and no difference were found for the gene expression of IL-6 among all treatments(P>0.05).4)There were no significant differences on cytokine cell proliferation index and apoptosis of splenic(P>0.05).(Conclusion)In conclusion,dietary supplementation of DHA could improve the immune function of laying hens when the added amount is less than 2.7 mg/g.Experiment 3.Evaluation of the tolerance of DHA from different sources in laying hensThe experiment was conducted to observe the effects of dietary DHA of Microalgae oil and Fish oil on performance,blood routine examination,plasma biochemical parameters,organs coefficients,tissue pathology slices and antioxidant capacity,with the aim to evaluate the tolerant dose of DHA on laying hens.Experiment 3.1 Five hundred and forty Hy-Line Brown laying hens of 31-week-old with similar laying rate were randomly allotted into 6 groups with 6replicates per groups and 15 hens per replicate.The laying hens in the control group were fed a basal diets without adding exogenous DHA sources,and the other five groups were fed the basal diets supplemented with 1.35,2.7,5.4,13.5 and 27 mg/g DHA(correspond with 0.25%,0.5%,1%,2.5% and 5% MO),respectively.The experiment lasted for twelve weeks followed an adaptation period of one week.The results showed as follows: 1)adding 13.5 mg/g DHA significantly decreased the egg production,average egg weight,egg mass(P<0.05),and feed/egg ratio was significant increased(P<0.05),27 mg/g DHA significantly decreased the ADF I(P<0.05).2)Dietary supplemented with 27 mg/g DHA did have a bad effect on AST?ALT and CRE,and serum TC,TG,LDL-C and HDL-C were decreased as dietary MO was increased(P<0.05).3)The 27 mg/g DHA group had a increased liver and kidney coefficients.4)Significant differences were observed in the content MDA of serum,egg yolk and liver among the 27 mg/g group and other groups.As a result,we suggest that the dose of MO in the feed of Hy-line Brown hens during the peak period should be less than 2.5%,that is,the amount of DHA from MO should be less than 13.5 mg/g.Experiment 3.2 Hy-Line Brown laying hens(n=450,31 week-old,near weight and egg production)were randomly allotted into 5 groups with 6replicates per groups and 15 hens per replicate.The laying hens in the control group were fed a basal diets without adding exogenous DHA sources,and the other five groups were fed the basal diets supplemented with 0.67,1.35,2.7 and 5.4 mg/g DHA(correspond with0.54%,1.08%,2.17% and 4.34% FO),respectively.The experiment lasted for twelve weeks followed an adaptation period of one week.The results showed as follows: 1)adding 5.4 mg/g DHA significantly increased the feed/egg ratio(P<0.05),there were no significant differences on egg production,average egg weight,egg mass(P>0.05).2)The TC?TG?LDL-C and HDL-C in serum were significantly decreased and VLDL was significantly increased(P<0.05)at DHA treatments.3)The 5.4 mg/g DHA group had a increased liver and kidney coefficients(P<0.05).4)Significant differences were observed in MDA of serum,egg yolk and liver among the 5.4 mg/g DHA group and other groups(P<0.05).As a result,we suggest that the dose of FO in the feed of Hy-line Brown hens during the peak period should be less than 4.34%,that is,the amount of DHA from FO should be less than 5.4 mg/g. |
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