Saccharomyces cerevisiae CELL WALL SUPPLEMENTATION ON GROWTH PERFORMANCE AND IMMUNITY STATUS OF WHITE SHRIMP Litopeneaus vannamei
The objective of this study was to evaluate effects of prebiotic (Saccharomyces cerevisiae cell wall) dietary supplementation on growth performance, survival rate, and on immune status and disease resistance against Vibrio harveyi and Vibrio parahemolyticus (agent of Early Mortality Syndrome disease "EMS") of shrimp Litopeneaus vannamei.
The shrimps were distributed in a completely randomized design, with 4 treatments; 0, 0.25, 0.5 and 1.0% of yeast product (Saccharomyces cerevisiae cell wall - ImmunoWall® from ICC Company, Brazil), with 8 replicates, being 4 replicates for growth performance and other 4 replicates for study on immunity (bacteria challenge). Each replicate consisted of 1,000L fiber tank with stocking density of 60 pieces/m2 in brackish water of 12-15 ppt. Shrimps of 6.45±0.26g were acclimated for one week, and then allocated to treatment tanks. The growth parameters measured were total feed intake (TFI, g/tank), feed intake (FI, g/ind.), daily feed intake (DFI, g/ind./d), production (g/tank) body weight (BW, g/ind.), body weight gain (BWG, g/ind.), average daily gain (ADG, g/ind./d), specific growth rate (SGR, %/d), feed conversion ratio (FCR), survival rate (SR, %), and at 14 and 28 days. The immunological parameters: total hemocyte count (THC, X105cell/ml), hemolymph protein (HP, ml/dl), and phenol oxidase activity (POx, unit/mg protein) also were measured at 14 and 28 days. For each bacteria challenge, after shrimp was fed with experimental feed for 1 month, 30 shrimps from each treatment were sampling to challenge with pathogenic bacteria by intramuscular injection. Infection dose was 2.6x 106 CFU/mL of Vibrio parahemolyticus and 1.0x 106 CFU/mL of Vibrio harveyi. Three hours after injection, shrimp hemolymp was collected for determining the immune response and evaluating the bacteria clearance ability, which was the efficiency of yeast cell wall to enhance the shrimp immune defense system. The mortality rate (MR, %) was determined every day, for 7 days.
Yeast supplementation at 0.5 and 1.0% improved (P<0.05) BW at 14 days, and TFI, FI and DFI at 28 days (Table 1). Regarding the immunological results, HP at 7 and 14 days, and POx at 21 days improved (P<0.05) at all yeast product levels supplemented when compared with control group. After V. harvey challenge the MR were significantly lower (P<0.05) in groups fed with yeast, at days 2 and 3 after challenge. Also THC and HP were significantly high (P<0.05) in groups fed with 0.5 and 1.0% of prebiotic (Table 2). For V. parahemolyticus challenge, shrimp THC improved in all yeast-supplemented levels (Table 2). In general, 0.5 and 1.0% of Saccharomyces cerevisiae cell wall promoted a better immunological support reflecting on lower mortality rates (55.6 and 77.8% lower than control, for 0.5 and 1.0%, respectively), though not statistically different, after V. parahemolyticus infection. This was also reflected in shrimp performance that was improved at 15 and 6.5% (0.5 and 1.0% average results) for BWG and FCR at 28 days.
The yeast cell wall supplementation at 0.5 and 1% in shrimp diets have improved body weight gain and feed intake. The inclusion rate of 1% of yeast cell wall enhance some immunity parameters under disease challenge condition by Vibrio harveyi and Vibrio parahemolyticus.