Apparent digestibility of crude protein and apparent availability of individual amino acids in tilapia (Oreochromis niloticus) fed phytase pretreated soybean meal diets

Soybeans contain phytates, the anionic forms of 1,2,3,5/4,6-hexakis (dihydrogen phosphate) myoinositol, with the potential to reduce amino acid (AA) availability. Tilapia lack the intestinal enzyme phytase to hydrolyze phytates. Oreochromis niloticus (approximately 68 g) were fed diets containing either phytase pretreated or untreated soybean meal (SBM) incorporated at 0, 25, 50, 75, or 100% of the crude protein (CP) in a 33% CP diet to determine whether phytates reduce CP digestibility and AA availability. There were no differences in apparent CP digestibility. Dietary and available methionine (Met), and available lysine (Lys), decreased with increasing incorporation of phytase pretreated SBM. Reduced availability of Met and Lys from the phytase pretreated diets was likely due to removal of phytates. Phytates may reduce the effect of other antinutritional factors, protect amino acids from degradation, or decrease leaching of water soluble components.