The current study was conducted to evaluate the synergetic effects of heat-killed Lactobacillus plantarum (HK L-137) and β-glucan (BG) on digestive enzyme activity and intestinal morphology of genetically improved farmed tilapia (GIFT) with focus on insulin-like growth factor I (IGF-I), fatty acid synthase (FAS), and glucose-6-phosphate dehydrogenase (G6PD). For 12 weeks, fish fed the control, or three diets incorporated with 100 HK L-137, 100 BG, or 50 HK L-137 + 50 BG mg/kg (HK L-137, BG, and HK L-137/BG diets). After final sampling, fish fed HK L-137 or HK L-137/BG diets exhibited significantly (P < 0.05) increased final body weight and weight gain while the specific growth rate and feed efficiency ratio enhanced only in HK L-137/BG group. Mucosal and villi lengths and muscle thickness significantly (P < 0.05) increased by HK L-137 or/and BG for the middle intestine. Lipase and protease improved significantly (P < 0.05) in fish fed both HK L-137 and BG when compared to the control group. Interestingly, qRT-PCR revealed a significant (P < 0.05) upregulation in the IGF-1 gene expression in fish fed HK L-137 or/and BG additives compared to the control. Muscle and liver G6PD gene expression were upregulated significantly (P < 0.05) in fish fed HK L-137/BG diet as compared to the control group. In addition, feeding HK L-137 or both additives effectively elevated the hematocrit, hemoglobin, and WBCs and decreased triglyceride and glucose levels. Accordingly, the use of both HK L-137 and BG is an efficient scheme to reach economically feasible and sustainable tilapia production.
Keywords: Digestive enzyme activity; Fatty acid synthase; GIFT tilapia; Glucose-6-phosphate dehydrogenase; HK L-137; Insulin-like growth factor 1; Intestinal morphometry; β-Glucan.