| The experiment was conducted to examine the effects of different conjugated linoleic acid(CLA) levels on nutrient repartition, growth performance, lipid metabolism, immunity competence, fatty acid composition in belly fat and breast & thigh muscle of Avain broiler chickens, and furtherly to investigate the function mechanism of CLA on above parameters. Three hundred and sixty Avain broilers (180^,180$) with the similar initial body weight (P>0.05) were averagely assigned to five groups with three replications (72 broilers) per group according to a Completely Random Design. The whole experiment lasted for 49 days. Different groups were fed diets with different CLA levels(0,0.5%,1.0 0%,1. 50% and 2.0 0%)., Which was supplied by the CLA oil.(containing 80% CLA). The details were as follows: Group I (the control group): the basal diet (containing 2.5% soybean oil and 0.00%CLA). Group II (0.50% CLA): 0.625% soybean oil in basal diet was substituted with 0.625%CLA oil (containing 1.875% soybean oil and 0.50% CLA) Group 111(1.00% CLA): 1.25% soybean oil in basal diet was substituted with 1.25%CLA oil(containing 1.25 soybean oil and 1.00% CLA). Group rV(1.50% CLA): 1.875% soybean oil in basal diet was substituted with 1.875%CLA oil (containing 0.625% soybean oil and 1.50% CLA). Group V(2.00% CLA): 2.50% soybean oil in basal diet was substituted with 2.50%CLA oil (containing 0.00% soybean oil and 2.00% CLA). The results showed that: (1) In the experiment, it was showed that CLA -had the function of nutritionalrepartition and could decrease the percentage of belly fat, increase the percentage of breast & thigh muscle, improve the content of fat and protein in the breast muscle, and elevate the meat quality of broilers. It was suggested that the nutritional repartitioning function of CLA was due to the elevated secretion of GH, INS, T3and T4.(2)Actually, SFA and CLA content of adipose tissue of broilers was significantly increased ( p < 0.05 ) and MUFA was significantly decreased ( p < 0.05) .however, CLA had no effect on PUFA(P>.05). The results of the composition of lipids in blood of broiler indicated that CLA could increase the ratio of HDL to LDL(P>0.05).It implied that CLA might has the effect of antiatherosclerosis, which needed to be justified.(3) Suitable content of CLA in the diets (below 1.50%) on the whole stage could improve average body weight, average daily gain and feed efficiency, and decrease the ratio of feed to gain, but had no significant effect on feed intake(P>0.05). Feed intake, average daily gain and growth performance were all restricted when the CLA in diets increased to 2% at the starter phase(0~35d). Although the average daily gain of broilers was significantly improved at the grower phase (36-49d) (p < 0. 05) when the broilers are adaptable to the diets, the growth performance on the whole stage was restrained because of the west restriction of 2% CLA at starter pahse..'(4) The results of immunity index indicated that CLA could stimulate the development of immune organs, improve the function of hormones immunity and cell-mediated immune competence.(5) Based on the above results, it is suggested that the optimal level of CLA in the diet of broiler chickens is 1.0%.
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