Effects of dietary zinc on growth, serum non-specific immune indexes, disease resistance and intestinal flora structure in juvenile Litopenaeus vannamei

The trial was conducted to study the effects of dietary zinc (Zn) on growth, non-specific immune indexes, disease resistance and intestinal flora structure in juvenile Litopenaeus vannamei. Zinc sulfate heptahydrate (ZnSO₄·7H₂O) was used as the Zn source in this experiment. The healthy prawns initial body weight (0.45±0.01) g were fed diets (isonitrogenous and isolipid) containing available Zn levels (i.e., 0, 20, 40, 60, 80, 100, and 150 mg/kg) for 8 weeks, respectively. The results showed that: ① The weight gain rate (WGR) and specific growth rate (SGR) in the 60 mg/kg group were significantly higher than those in the control group, and the best feed conversion rate (FCR), the optimal protein efficiency ratio (PER) and survival rate (SR) were found in 80 mg/kg group.② The crude lipid (CL) contents in 80-150 mg/kg groups were significantly higher than that in control group, and the contents of crude ash (CA) in 40-80 mg/kg groups were significantly higher than that in control group.③ The contents of serum total protein (TP), total cholesterol (TC) and triglyceride (TG) in Zn supplemented groups were significantly higher than those in control group. ④ Dietary Zn supplement increased the activities of serum superoxide dismutase (SOD), phenol oxidase (PO), alkaline phosphatase (AKP) and acid phosphatase (ACP) and total antioxidant capacity (T-AOC), and significantly decreased the content of malondialdehyde (MDA) in serum, indicating that Zn could improve the non-specific immunity of L. vannamei.⑤ In the experiment of artificial acute infection with Vibrio harveyi, the survival rate of shrimp increased firstly and then decreased with the increase of Zn levels. The survival rate in Zn supplemented group was significantly higher than that in control group, and the highest survival rate and disease resistance were found in 80 mg/kg group. ⑥ In the analysis of intestinal flora, the numbers of effective OTUs in 40 mg/kg and 100 mg/kg groups were significantly higher than that in control group. With the increase of dietary Zn, the Ace index and Chao1 index increased significantly, while the Shannon index and Simpson index had no significant changes. The results showed that an optimal level of Zn could promote the growth and improve the disease resistance of juvenile L. vannamei. The growth performance and disease resistance of L. vannamei were poor when Zn was deficient in diets, while excessive Zn level inhibited the growth of L. vannamei to a certain extent. Overall, based on the WGR, the growth performance of L. vannamei was significantly improved by supplementing 94.46 mg/kg Zn to the diets. Based on the evaluation of disease resistance, the optimal dietary Zn supplement of L. vannamei was 80 mg/kg.