Impacts of β-Mannanase on Fecal Viscosity, Digestible Energy Content, Amino Acid Digestibility, and Nutrient Loss in Juvenile Nile Tilapia Fed Soybean Meal-Rich Diets

This study evaluated the impact of increasing dietary β-mannanase (BM) supplementation (Natupulse TS, BASF, Ludwigshafen am Rhein, Germany) on fecal viscosity and pH, apparent digestibility coefficients (ADCs) of energy and nutrients, including amino acids, fecal nutrient loss in contents of soybean meal (SBM)-based diets fed to juvenile Nile tilapia, Oreochromis niloticus. A total of 504 fingerlings (initial body weight of 31.5 ± 4.2 g) were randomly distributed into 24 aquaria (70 L each) in a completely randomized design using six dietary treatments and four replicates of 21 fish per aquarium. Fish were fed diets containing BM at 0, 1600, 3200, 4800, 6400, and 8000 TMU (thermostable endo-1,4-BM units) kg⁻¹ and hand-fed six times a day until apparent satiety for 30 days. Chromium oxide was employed as an indigestible marker. The ADC of gross energy, crude protein, crude lipids, and essential amino acids exhibited a quadratic effect with the maximum point in fish fed 4818, 4722, 4615, and 4816 TMU kg⁻¹ BM, respectively. The digestible energy (DE) content of diets presented a quadratic effect, and the maximum point was obtained in fish fed 4803 TMU BM kg⁻¹ diet, which improved the DE content by +1.2 MJ kg⁻¹ relative to the BM-unsupplemented diet. The fecal pH, fecal viscosity, organic matter loss, and nitrogen loss presented a quadratic effect with the minimum point in fish fed 4810, 4839, 4750, and 4801 TMU BM kg⁻¹ diet, respectively. Principal component analysis indicated that dietary BM at 4800 and 6400 TMU BM kg⁻¹ diet was associated with improvements in the ADC of gross energy, crude protein, and crude lipids. In conclusion, including 4803 TMU BM kg⁻¹ diet effectively improves DE content and optimizes nutrient digestibility and feces pH and viscosity in Nile tilapia fed an SBM-based diet.