The effect of phytase on apparent digestibility of four practical plant feedstuffs fed to striped bass, Morone saxatilis

This study was conducted to determine the effect of phytase on apparent dry matter (DM), crude protein and phosphorus (P) digestibility of four plant feedstuffs (isolated soya protein, ISP; soyabean meal, SBM; corn gluten meal, CGM and wheat middlings, WM) fed to striped bass Morone saxatilis . One reference diet was formulated based solely on animal feed ingredients. Four test diets were prepared by mixing 60–75% of the reference diet with 40–25% of the test ingredient in order to reach similar levels of total P (0.67–0.73%) and to have a minimum of 35% protein (36.1–53.0%). Chromic oxide was added at 0.5% of the diet and used as an indigestible marker. A phytase solution was sprayed postpelleting on the test diets at a concentration of 1000 phytase units kg⁻¹ (PU kg⁻¹) dry diet. The test diets (with or without phytase supplementation) and the reference diet (nine treatments total) were fed to 3-year-old striped bass and were replicated in time ( n =3) during the 4-week period. Digestibility of DM was significantly lower ( P  < 0.001) for SBM and WM when compared with CGM and ISP and was not influenced by phytase supplementation. Crude protein digestibility was also not affected by phytase supplementation and was significantly lower ( P  < 0.09) for SBM when compared with ISP. Phosphorus digestibility was improved by approximately 23% with the addition of phytase for all four feedstuffs tested ( P  < 0.001). Furthermore, WM had significantly lower ( P  < 0.0001) P digestibility when compared with the other feedstuffs, irrespective of phytase supplementation.