| Two trials were conducted to evaluate the effect of feeding 40 mg/kg zinc, from zinc sulfate heptahydrate(Zn-S), methionine hydroxy zinc(Zn-M), glycine zinc(Zn-G),Meiduo-C-A(Associative type, Zn-C-A), Meiduo-C-B(Coated form, Zn-C-B), on growth performance, physiological and biological indices in serum and Zn concentration in tissues of Litopenaeus vannamei, on the other hand, to determine the optimum dietary requirement of feeding 0, 10, 20, 40, 60, 80 mg/kg zinc with zinc sulfate heptahydrate(Zn-S), methionine hydroxy zinc(Zn-M) as Zn sources. The results were summarized as follows:Experiment 1. A total of 720 experimental shrimp with an average initial weight of0.340±0.001 g were selected and reared in the 380 L fiberglass tanks with six treatments(3 duplicates per treatment and each duplicate had 40 larvaes). The control group was fed basal diet with fish meal, soybean meal, peanut meal and corn gluten meal as the source of protein, test groups were fed diets added 40 mg zinc/kg from Zn-S, Zn-M, Zn-G,Zn-C-A and Zn-C-B on the basis of basal diet. Results of the 8-weeks rearing experiment indicated that the same supplement of different Zn sources had a significant effect on growth performance of Litopenaeus vannamei. The best and the lowest weight gain rate(WGR), specific growth rate(SGR), protein efficiency rate(PER) and feed conversion rate were found in Zn-M group and control group(DZ), respectively, and there was significant difference in those indices between Zn-M group and control group(P<0.05).Different Zn sources significantly affected the content of crude lipid(CL) and crude ash(CA) of the whole shrimp(P<0.05), but did not affect the content of moisture and crude protein(CP)(P>0.05). Total protein(TP) of serum in Zn-C-B group was the highest,Zn-M group ranked second.And then, triglyceride and cholesterol content of serum in Zn-S group were the highest. The non-specific immune enzymes activity(such as T-SOD,ACP, AKP, PO) in Zn-M group were higher than that in other groups. These results suggested that Zn-M is able to promote the growth and immunity of Litopenaeus vannamei effectively than other four Zn sources,then regarded as the suitable Zn sourcefor Litopenaeus vannamei.Experiment 2. A total of 1320 experimental shrimp with an average initial weight of0.340±0.001 g were selected and reared in the 380 L fiberglass tanks with eleven treatments(3 duplicates per treatment and each duplicate had 40 larvaes) sharing the same control group. The control group was fed basal diet with fish meal, soybean meal,peanut meal and corn gluten meal as the source of protein, test groups were fed diets added 10, 20, 40, 60, 80 mg zinc/kg from Zn-S and Zn-M on the basis of basal diet.Results of the 8-weeks rearing experiment indicated that whatever Zn sources and levels had no significant effect on SR(P<0.05). With the supplement of dietary Zn content, the WGR and SGR of Zn-S group increased first, then went steady. As to Zn-M group,the WGR and SGR showed the trend of declining after rising, when the supplemental level reached 40 mg/kg, WGR and SGR showed the trend of decline(P<0.05). FCR of two Zn sources experimental group was significantly decreased(P<0.05), when the Zn level reached 10 mg/kg, there was no significant difference among every experimental group(P>0.05). Different dietary Zn levels had significant influences on CP, CL and CA(P<0.05), Zn source and supplemental level had interaction in CA(P<0.05). This suggest that dietary Zn can change the body composition of the whole shrimp. TP, TG and CHOL content in serum were significantly affected by dietary Zn content(P<0.05); Zn sources,dietary level and their interaction had significant influences on TG and CHOL content(P<0.05). With the dose increasing of Zn, the activities of ACP and AKP increased first,then decrease; the activities of T-SOD and PO increased first, then went steady; Zn concentration in the whole body and in the muscle showed the trend of increase, then declined. Based on WGR, whole body and muscle Zn content, by quadratic curve or broken line analysis showed that optimum dietary Zn levels respectively were 93.36mg/kg and 66.03 mg/kg; 71.48 mg/kg and 69.29 mg/kg; 95.06 mg/kg and 58.69 mg/kg. |
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