Dose-Response Curves for the Effects of Lactobacillus plantarum on Growth Performance, Feed Utilization, and Health Status of Litopenaeus vannamei Shrimp. Optimizing the Economic Efficiency of Supplementation

A 14-week feeding trial was conducted to employ polynomial regression analysis to establish the optimal dosage of Lactobacillus plantarum (Lac) for enhancing the growth performance, digestive enzyme activities, and blood biochemical, redox balance, and immunity response of Litopenaeus vannamei shrimp (initial body weight = 2.94±0.03 g). A total of 240 healthy Litopenaeus vannamei shrimp were randomly distributed into four equal groups and were fed diets containing 0, 200, 400 and 800 mg Lac/kg diet respectively for 98 days. Increasing the levels of dietary Lac cubically improved growth performance and feed utilization (P<0.01), the optimal doses were established at 600 and 650 mg Lac/kg diet, respectively. Muscles thickness decreased significantly in all treated group compared to the control (P<0.05). The dietary treatment quadratically affected total protein (P<0.0001), triglycerides (P<0.0001), and cortisol (P=0.0097), the optimal responses were observed at 650, 700, and 600 mg Lac/kg diet, respectively. Meanwhile the activities of liver enzymes (ALT and AST), the levels of blood urea and digestive enzymes (amylase and proteases) were cubically enhanced by the treatment, the optimal dosages were at 600 and 650 mg Lac/kg diet for liver enzymes, and urea concentration, respectively and at 650 and 700 mg Lac/kg diet for the activities of amylase and protease, respectively. With regards to redox balance, increasing the levels of Lac caused a quadratic decrease in the levels of malondialdehyde (P=0.0398) and a cubic increase in the activities of superoxide dismutase (P=0.0265), and catalase (P=0.0163), the corresponding dose–response curves showed that the optimal dose was at 650 mg/kg diet. However, the levels of total antioxidant capacity were in a quadratic increase (P=0.0372), maximizing at a level of 600 mg Lac/kg diet. Concerning the immunity response, both lysozyme and IgM were significantly affected by the dietary treatment (P=0.0002 and 0.0001, respectively), maximizing at 600 and 650 mg Lac/ kg diet, respectively. Dietary supplementation of Lac had significant and substantial impacts on the economic efficiency (P<0.0001). In conclusion, the dietary inclusion of 600–700 mg Lac/kg diet can be used as an effective and practical feeding strategy to enhanced growth performance, feed efficacy, redox balance and nonspecific immune responses in Litopenaeus vannamei shrimp.