Dietary carbohydrates and protein of yeast modulate the early stages of innate immune response in tilapia (Oreochromis niloticus) primarily after LPS inoculation

The administration of yeast-derived immunostimulants leads to improvement of the immune system and growth performance preventing the antibiotics misuses. The objective of this study was to evaluate the effects of dietary Actigen® [0, 0.04, 0.06 and 0.08 % of Actigen (ACT)], on the immunological and physiological responses and growth performance of tilapia after lipopolysaccharide (LPS) inoculation. The experiment was conducted in two trials. In the first trial, the ACT was offered for 30 and 60 days; in the second trial, the ACT was offered for 60 days, and then fish were challenged by intraperitoneal injection with LPS and sampled at 5 and 12 days after inoculation. After the first trial, immunological, hematological and biochemical parameters, intestinal morphology and the growth performance were assessed, whereas in the second trial, immunological, hematological and biochemical parameters were assessed. Supplementation of diets with ACT showed a significant effect mainly after 60 days of feeding, with increased lysozyme, globulin, HTC, MCV, erythroblasts, leukocytes, lymphocytes and monocytes. A general decrease in cells and globulin occurred at 5 days after the LPS challenge, with partial recovery at 12 days after the challenge. In addition, the study demonstrated that the use of ACT, an extract derived from yeast cell walls and containing active mannan protein and carbohydrates, effectively increased the immune parameters evaluated, indicating a possible beneficial effect on fish health.