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This study was conducted to investigate the effect of conjugated lionleic acid (CLA) on carcass characteristics,composition of fatty acid,blood biochemical index, lipids metabolism, antioxidant ability and immuno function in broilers, to explain the mechanism preliminarily and to determine the best adding dose and period of CLA,so that offer theory for development.Six hundred and thirty 1-day-old healthy Ross broilers were randomly divided into seven treatments and each treatment was replicated using three cages containing thiry broilers per cage and the experiment lasted forty-two days.The broilers were fed seven dietary treatments containing 0%, 0.3%, 0.6%, 0.9%, 1.2%, 1.5% or 1.8% CLA.Soybean oil and CLA source were substituted on a weight basis in different diets.After 2 weeks,4 weeks and 6 weeks dietary treatment,every treatment 12 birds were slaughted to collected samples to test.The results of the experiment are that:①Adding 1.2% to 1.5% CLA could raising feed utilization efficiency significantly in whole experiment period.Compared with the control,the feed conversion ratio V and VI was decreased by 5.39%(P<0.05) and 6.27%(P<0.05).②CLA could be improve nutritient digestive ratio of broilers. Compared with control groups, the Cp digestive ratio has been increased in every experiment group, but has not be remarkable expect VI and VII significantly increased by 9.04% and 8.51% respectively, calcium was increased by 11.75%(P<0.05), 27.09%(P<0.01), 29.69%(P<0.01), 34.21%(P<0.01), 39.10%(P<0.01), 45.99%(P<0.01) has significantly or extremely significantly, and phosphorus was increased by 0.98%, 5.53%, 9.66%(P<0.05), 19.27%(P<0.01), 18.14%(P<0.01), 11.47%(P<0.05), IV has obvious difference,V,VI,VII has extremely significantly.③When CLA added over 1.0%(V, VI, VII) could obvious enhance muscle rate and reduced abdomen fat rate, compared with control group,at 14 day V, VI, VII the muscle rate has been increased by 11.22%(P<0.05), 16.50%(P<0.05), 24.19%(P<0.01) and abdomen fat rate has been decreased by 22.73%(P<0.05), 38.96%(P<0.01), 53.90%(P<0.01), at 28 day V, VI, VII the muscle rate has been increased by 8.09%(P<0.05), 9.06%(P<0.05), 11.05%(P<0.05) and abdomen fat rate has been decreased by 31.65%(P<0.01), 44.24%(P<0.01), 53.60%(P<0.01), at 42 day V, VI, VII the muscle rate has been increased by 8.78%(P<0.01), 8.57%(P<0.01), 8.62%(P<0.01) and abdomen fat rate has been decreased by 28.98%(P<0.01), 27.27%(P<0.01), 15.91%(P<0.05). The older the smaller of muscle fiber density, the biger of muscle fiber area and diameter, adding above 1.0% is better.④CLA could improve CLA contend in muscle,liver and abdomen and change the composition of fatty acid.CLA content from 0% increased to 1.07%, 2.14%, 3.11%, 3.71%, 4.56%, 5.58% in muscle, from 0.05% increased to 0.69%, 1.52%, 1.88%, 2.54%, 2.78%, 3.25% in liver and from 0.40% increased to 3.16%,4.66%,7.52%,9.04%,12.38%,12.62% in abdomen respectively, all of them has extremely significantly compare to group I.Test with faeces showed CLA content is 0.73%, 0.61%, 0.54%, 0.39%, 0.28%, 0.51%, 0.62% respectively. So when added 1.2% is best. Test CLA deposition content in muscle, liver, abdomen at 14,28,42d found when at 28 day is highest.⑤CLA could regulated lipid metabolism, decreased TG, TCHO, LDL, NEFA and increased HDL of blood, increased LPL and HL of liver. In each adding group , TG has been decreased by 15.7%(P>0.05), 28.1%(P<0.05), 32.2%(P<0.05), 57.0%(P<0.01), 40.0%(P<0.01), 51.2%(P<0.01) group V is best, TCHO has been decreased by 13.3%(P>0.05), 16.1%(P<0.05), 22.2%(P<0.01), 23.5%(P<0.01), 19.2%(P<0.05), 16.7%(P<0.05), LDL has been decreased by 15.7%(P>0.05), 21.2%(P<0.05), 27.8%(P<0.01), 31.3%(P<0.01), 26.3%(P<0.01), 24.7%(P<0.01), NEFA has no different except group III. LDL in group V and VI is higher has been increased by 32.1% and 31.1% has extremely significantly(P<0.01). LPL and HL is highest in V when added 1.2%.⑥Added 1.2%~1.5% CLA could improve the immuno-organs development remarkable TP, ALB, GLO, A/G and urea-n has no different V is best,IgG and IgM has been increased significantly.⑦CLA could improve the antioxidant ability, increase plasma SOD and GSH-Px decrease MDA. Compared with control group, GSH-Px has been increased by 8.33%(P>0.05), 11.03%(P<0.05), 20.38%(P<0.05), 70.72%(P<0.01), 61.19%(P<0.01), 16.73%(P<0.05), SOD has been increased by 2.67%(P>0.05), 15.95%(P<0.01), 23.45%(P<0.01), 26.61%(P<0.01), 27.49%(P<0.01), 8.98%(P<0.05), MDA has been decreased by 14.16%(P<0.05), 13.65%(P<0.05), 5.31%(P<0.05), 29.85%(P<0.01), 32.02%(P<0.01), 23.72%(P<0.01) respectively. Considering all factors,adding CLA could improve on growth performance of broilers,change composition of fatty acid, effect lipids metabolism ,improve immune performance and antioxidant ability.Adding 1.2% CLA at 28 days before sale is best.
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