Factors affecting nutrient digestibility in rainbow trout (Oncorhynchus mykiss) fed a plant protein-based diet supplemented with microbial phytase

Factors influencing apparent digestibility coefficient (ADC) of nutrients from a plant protein–based diet supplemented with microbial phytase were investigated in a series of experiments with rainbow trout (Oncorhynchus mykiss). The influence of phytase level, water temperature, feed particle size and addition of a protease/non-starch polysaccharidase (PNSP) enzyme cocktail were tested in a phytase-supplemented (2000 FTU kg−1) diet. Finally, the influence of Ca/P ratio, addition of 1,25-hydroxycholeocalciferol, or inclusion of lactic acid (LA) in diets with and without phytase was evaluated. Addition of microbial phytase improved ADC of dry matter (DM), protein, ash and minerals (P, Ca, Mg, Fe and Zn) (P < 0.05). Reducing feed particle size potentiated the effect of phytase on P and ash ADC, as did the addition of a PNSP enzyme cocktail; the latter also significantly improved DM ADC in both control and phytase-supplemented diets. Increasing the Ca/P ratio reduced the effect of phytase on P and ash ADC. Addition of 1,25-dihydroxycholecalciferol and LA had no effect on DM, P and ash ADC in control diets and tended to reduce the phytase-induced increase in P ADC.