Effects of dietary zinc sources and levels on growth performance, serum biochemical and immunological indexes and tissue zinc content of Litopenaeus vannamei

Abstract

This investigation aimed at estimating the effects of two zinc (Zn) sources and dietary Zn levels on growth performance, serum biochemical and immune indexes and zinc content of tissues. There were two Zn sources, Zn sulphate heptahydrate (Zn-S) and Zn methionine (Zn-M) with five addition gradients (10, 20, 40, 60, 80 mg/kg), separately, added to the isonitrogenous and isolipidic basal diets. The group without additional Zn supplement served as the control group. In the eight-week experiment, Litopenaeus vannamei (0.34 g initial body weight) was fed 11 kinds of experimental diets respectively (shared control group) for 8 weeks. The results indicated that: 1) dietary Zn-S and Zn-M significantly improved weight gain rate (WGR), specific growth rate (SGR), protein efficiency rate (PER) of shrimp (P < 0.05). Feed conversion ratio (FCR) of both the Zn-S and Zn-M groups was distinctly reduced (P < 0.05). Zn sources and Zn levels and the interaction of them (IZSL) didn't distinctly influence survival rate (SR) of shrimp (P > 0.05). WGR, SGR, PER and FCR were not influenced by Zn sources and IZSL (P > 0.05) while they were significantly influenced by Zn levels (P < 0.05). 2) Contents of body crude protein (CP), crude lipid (CL) and crude ash (CA) were remarkably affected by dietary Zn levels (P < 0.05), and CP content of the body was significantly affected by Zn sources. IZSL had an impact on CA content (P < 0.05). 3) Contents of triglyceride (TG) and cholesterol (CHOL) in serum were significantly increased by dietary Zn-S and Zn-M (P < 0.05), and simultaneously, activities of acid phosphatase (ACP), alkaline phosphatase (AKP) and total superoxide dismutase (SOD) in serum were improved by dietary Zn-S and Zn-M (P < 0.05). There were distinct effects of IZSL on serous activities of ACP and AKP (P < 0.05). 4) Content of Zn in the body and muscle were significantly increased by dietary Zn-S and Zn-M (P < 0.05). Zn content of muscle was significantly affected by Zn sources, but Zn content of body and muscle were not influenced by IZSL (P > 0.05). In conclusion, dietary Zn-M and Zn-S both improved growth performance and immunity of shrimp. Based on WGR and Zn content of the whole body, the optimum requirements of Zn in Zn-S or Zn-M for shrimp were 93.36 ~ 112.28 mg/kg and 66.03 ~ 103.61 mg/kg. Additionally, Zn-M exhibited higher avail and immunity and was recommended in diets of Litopenaeus vannamei.