| 4-week-old Jin-Ding growing ducks (n=216) with similar weight (0.45±0.01) kg were randomly allotted into six treatments with six replications and six ducks each in a completely randomized design. The growing ducks were exposed to 1 of the 6 treatments as follows: the basal diet was same and without adding vitamin E, six treatments were fed vitamin E supplemented with 0, 10, 20, 40, 100 IU/kg respectively relative to the basal diet. The entire trial period was 7 weeks. In the experiment, the laying ducks were weight at the beginning and the end. For each replicate group, ducks weight and surplus feed were record each two weeks to calculate daily gain and feed conversion ratio. At the end of the feeding trial, 6 ducks which weight closely in each treatment were randomly chosen and collect blood through jugular artery puncture, and killed to take out the liver and immune organs including spleen, bursa and thymus. Which to determin the immunity, antioxidant and metabolic hormones of serum and tissue and calculate the immune organ indexes.The results of growth showed that vitamin E supplement had no significant influence on ADG and FI (P>0.05), however, with the vitamin E levels increasing, ADG of growing ducks rose and then reduced and FI had the opposite tendency, first reduced and then increased, the best addition level is 15～20IU/kg. Addition of 15～20IU/kg vitamin E in diet had significant decreased F/G compared to control group (P<0.05).The results of organism biochemistry index indicated that there was no significant influence on serum Ca, P, Na, K, Cl content and ALP, LDH activity to growing ducks with vitamin E supplementation increasing. There were no significant difference but has a different degree increase of T-AOC and GSH-Px activity in serum and liver (P>0.05), addition of 15, 20 IU/kg vitamin E in diet had an significant increase SOD activity in serum compared to those added with 0, 10IU/kg vitamin E group (P<0.05), but excessive vitamin E level had decreasing tendency. However, MDA in serum had decreasing tendency and no significant difference (P>0.05), but content of MDA in liver decreased significantly (P<0.05) when addition of 40IU/kg vitamin E in diet. Concentration of a-tocopherol in serum and liver increased with vitamin E levels increased. Concentrations of serum Immunoglobulin (A, G, M), IL-2, ALB, GLO and TP increased with vitamin E levels increased, the effect was better when the addition level was 15, 20 IU/kg but there was no significant difference (P>0.05). Each treatment of immune organ indexes (thymus, bursa and spleen) had a different degree increase compared to those added with 0 IU/kg vitamin E group, significant effects on immune organ index (thymus and bursa) were observed in growing ducks fed supplemental 15, 20 IU/kg vitamin E in diet (P<0.05). Ducks fed the diets supplemented with 15, 20 IU/kg vitamin E group concentration of serum GH had significant difference compared with no addition of vitamin E group (P<0.05), but concentration of Cort had the opposite tendency relative to the vitamin E levels, addition of 15 and 20 IU/kg vitamin E in diet had lower concentration than other groups. Concentrations of serum T3 and T4 had higher than the group of no supplemented obviously, but there was no significant difference (P>0.05).According to the growth, serum biochemical indexes and organism antioxidant, immunity and metabolic hormones indexes variety analysis of the same term, addition of 15 IU/kg vitamin E in the corn-soybean meal diets (vitamin E calculated 4.9 IU/kg) which can satisfy the growth requirements, and moderate supplementation of vitamin E may enhance antioxidant, immunity and other biochemical indexes. It is suggest that the optimal supplement amount of vitamin E was from 15 IU/kg to 20 IU/kg under cage condition at the stage of young laying ducks.
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