Dietary combinations of L-threonine and encapsulated source of butyric acid (ButiPEARL) modulate growth, some physiological and biochemical parameters, histomorphometry of the intestine, and economic indices of Nile tilapia (Oreochromis niloticus) fingerlings

Background Various immunostimulants have been used as additives in fish feed because they enhance growth and immunity. The current work examined the impact of dietary L-threonine and an encapsulated form of butyric acid (ButiPEARL) on various aspects of Nile tilapia, Oreochromis niloticus ( O. niloticus ), including growth performance and immune response. Materials and methods: A total of six experimental fish groups (n = 80) were utilized. The fish in the control group (G1) were fed a basal diet, while those in the other groups were fed experimental diets. The feeding was done twice daily for 42 days, with the food given being 5% of the fish's body weight. The water parameters were maintained at suitable levels. Results The supplementation of these feed additives, particularly the group of fish fed a diet containing 0.3g/kg of encapsulated butyric acid (ButiPEARL) mixed with 0.48g/kg of L-threonine, exhibited the highest values throughout the experiment. This supplementation significantly enhanced growth performance indicators such as length gain, weight gain, weight gain rate (WGR), specific growth rate (SGR), and feed conversion ratio (FCR). Furthermore, it positively influenced immunological parameters (IgM, albumin, total protein in serum, and nitrous oxide in liver tissue), liver enzymes (ALT, AST in serum), antioxidants (superoxide dismutase and catalase, SDA) and malondialdehyde, MDA in the liver), biochemical assays (plasma glucose concentrations), and digestive enzymes (lipase and amylase) in plasma. Regarding fish farm profitability, a higher net profit can be achieved by maximizing returns while minimizing costs. The histology and scanning electron microscopy (SEM) analysis of the O. niloticus intestines revealed significant improvements in the length and width of the intestinal villi. Conclusion The inclusion of L-threonine (0.48g/kg) and encapsulated butyric acid (ButiPEARL) (0.3g/kg) in fish diets can serve as safe, natural, and cost-effective feed additives. A combined inclusion level of these additives is recommended to enhance growth, boost immunity, support liver function, and promote intestinal development.