Discontinuous Administration of β-glucan is Effective for Preventing Immune Fatigue in Litopenaeus vannamei

β-glucan is an effective, available immunostimulant that has been successfully used to improve the immune defense of shrimp against pathogenic infection. However, the long-term continuous use of β-glucan can lead to immune fatigue, and intermittent feeding may be an effective way of avoiding this phenomenon. A 60-day growth trial was conducted to compare the effects of different feeding strategies of diets containing 200 mg/kg β-glucan on the growth and immune system of the Pacific white shrimp Litopenaeus vannamei. The results showed that either continuous feeding or intermittent feeding of diets containing 200 mg/kg β-glucan did not promote the growth of L. vannamei. However, the levels of superoxide dismutase, alkaline phosphatase, and acid phosphatase in the hepatopancreas of L. vannamei in the intermittent feeding group were significantly higher than those in the control and continuous feeding groups. Expression levels of the genes encoding LPS/β-glucan binding protein, superoxide dismutase, lysozyme, penaeid in-3a, and catalase were also significantly upregulated in the intermittent feeding group, whereas most of the immune parameters in the continuous feeding group were not significantly different from those of the control group. After artificial infection with Vibrio parahaemolyticus, the average mortality rates in the control group, the continuous feeding group, and the intermittent feeding group were 76.67%, 78.89%, and 45.56%, respectively. The results indicated that the addition of 200 mg/kg β-glucan to the diet did not promote the growth of L. vannamei, but the strategy of intermittent feeding effectively prevented immune fatigue and enhanced disease resistance, perhaps by increasing nonspecific immunity in L. vannamei