Effect of microbial phytase on apparent nutrient digestibility of barley, canola meal, wheat and wheat middlings, measured in vivo using rainbow trout ( Oncorhynchus mykiss )

Microbial phytase (Natuphos 5000G) was supplemented into barley, canola meal, wheat and wheat middlings at 500 FTU kg –1 diet to test the effectiveness of the phytase on digestibility of crude protein (CP), gross energy (GE) and minerals for rainbow trout. A total of 180 rainbow trout (initial mean body weight 223.8 ± 17.9 g) were stocked into ten 40‐L fibreglass digestibility tanks with 18 fish per tank. Duplicate tanks were assigned to a reference diet and a single tank was assigned randomly to each of the eight diets made from these four ingredients supplemented with and without phytase. The collection of faeces lasted for 2 weeks. Faeces collected in each week represented a replicate and they were analysed separately. The mean apparent digestibility coefficients (average of four ingredients) in phytase supplemented and nonsupplemented ingredients were: CP, 97.3% and 96.5%; GE, 62.8% and 53.1%; calcium (Ca), 38.3% and –5.3%; magnesium (Mg), 72.4% and 50.3%; manganese (Mn), 31.0% and –4.2%; total‐phosphorus (total‐P), 71.1% and 47.6%; phytate‐phosphorus (phytate‐P), 87.5% and 22.3%; copper (Cu), 38.3% and 26.4%; potassium (K), 97.1% and 97.0%; sulphur (S), 90.2% and 88.6%; zinc (Zn), 12.3% and –16.6%. A two‐tailed t ‐test indicated that phytase supplementation significantly ( P  < 0.05) improved the digestibility of Ca, Mg, Mn, total‐P, phytate‐P, and GE. The efficacy of phytase on nutrient digestibility also depended on the type of ingredient as measured in rainbow trout.