Top-spraying xylanase and β-glucanase improves digestible energy content and optimizes protein and amino acids digestibility in high-fiber diet fed to growing Nile tilapia

Recent evidence has shown that the advantage of top-spray enzymes is to surmount the problem caused by high temperature during extrusion and drying processes and ensure high residual content of exogenous enzymes in extruded aquafeeds. This experiment aimed to investigate the effects of the liquid blend of xylanase and beta-glucanase (XB) on the apparent digestibility coefficient (ADC) of dry matter (DM), gross energy (GE), and nutrients including amino acids (AA), as well impacts on digestible energy (DE) and nitrogen retention (Nr) in low and high-fiber diets fed to growing Nile tilapia, Oreochromis niloticus. Fish (n = 192) were randomly assigned to 4 treatments in a 2 x 2 factorial design with 2 levels of fiber (low or high), either not supplemented (Control) or supplemented with XB (0.2 g/kg, contained analyzed 1130 TXU/kg of 1,4-beta-xylanase and 512 TGU/kg of 1,4-beta-glucanase). The chromium oxide was used as an indigestible marker. Data were obtained during 2 subsequent runs of feces collection of 10 days, run 1 (initial body weight of 60 g +/- 3.4 g), and run 2 (initial body weight of 72 +/- 3.7 g). Each diet was tested using 4 replicates with 2 replicates run. The low-fiber diet with XB exhibited significantly higher ADC of GE than other diets. However, the high-fiber diet containing XB revealed higher ADC of GE than that without XB addition. Compared to control, XB addition improved the ADC of dry matter (DM), crude protein (CP), calcium (Ca), and phosphorus (P). Relative to control, DE and Nr were notably higher in the XB-added diet by 0.41 MJ/kg and 0.21 g/kg diet, respectively. The highfiber diet containing XB showed equivalent ADC of Thr than the low-fiber diet without XB inclusion. The high-fiber diet with XB exhibited comparable ADC of Thr than the low-fiber diet without XB addition. The low-fiber diet showed increased ADC of all essential AA, except Lys and Met. However, compared to control, XB addition improved the ADCs of branched-chain AA, Lys, and Thr. Overall, liquid XB at 0.2 g/kg onto extruded pellets optimized digestibility, increased digestible energy, and retained N contents, mainly in the high-fiber diet. This study identified the potential of liquid XB to be used on an industrial-scale by application onto extruded pellets for precision Nile tilapia feeding.