Effect of enzymes (phytase and xylanase), probiotics (B. amyloliquefaciens) and their combination on growth performance and nutrient utilisation in Nile tilapia

The increased use of plant ingredients in aquafeeds over the last decades, as replacement for fish meal, has led to rising levels of undesired non-starch polysaccharides (NSP) and phytate. Both NSP and phytate degrading enzymes and probiotics have been widely studied. They can be used as a tool to deal with increasing levels of NSP and phytate in aquafeeds. However, studies combining both probiotics and enzymes are scarce in fish. The main objective of the present study was to assess the impact on Nile tilapia (Oreochromis niloticus) of enzymes and probiotics, as well as their synergistic effect. Parameters measured were: growth; nutrient digestibility; body composition; and the energy, nitrogen (N), P and Ca balance. Diets were supplemented with, and without, an enzyme mix (phytase at 1000 FTU/kg and xylanase at 6000 U/kg) and with, and without, probiotics (three strains of B. amyloliquefaciens at 60 mg/kg feed), according to a 2 × 2 factorial arrangement. This resulted in a control treatment (CON-CON) without enzymes and probiotics, an enzyme treatment (ENZ-CON), a probiotic treatment (CON-PRO) and a treatment with both enzymes and probiotics (ENZ-PRO). In total, 16 tanks (4 replicates/treatment) were used with 35 fish each (mean initial weight 39 g). Fish were restrictively fed equal amounts of dry matter for 42 days. Both enzymes (P < 0.001) and probiotics (P < 0.05) improved growth (g/d) and FCR when applied individually. The combination of enzymes and probiotics showed an interaction effect (P < 0.05) on growth and FCR. Enzymes improved growth to a greater extent than probiotics, whereas the combination of enzymes and probiotics did not further enhance growth. The CON-CON treatment had the highest FCR (1.33), the CON-PRO treatment a slightly lower FCR (1.27); the lowest FCR (1.11) was found for both treatments with enzymes (ENZ-CON and ENZ-PRO). Enzyme supplementation improved the digestibility of all nutrients (P < 0.01), whereas probiotics enhanced fat digestibility (P < 0.01). Additionally, enzyme supplementation increased retained P (mg/d), retained N (mg/d) and N efficiency (P < 0.001). Probiotic supplementation affected the energy requirements for maintenance (kJ/kg^0.8/d; P < 0.05). Dietary supplementation of either enzymes or probiotics had positive effects on the measured parameters, but the combination of enzymes and probiotics did not have a synergistic effect.