Effect of exogenous phytase on feed inositol phosphate hydrolysis in an in vitro rumen fluid buffer system

Three in vitro experiments using a rumen fluid buffer system were performed to investigate the effect of addition of 4 experimental phytases (Phy1, Phy2, Phy3, and Phy4) compared with no addition of phytase on feed inositol phosphate hydrolysis in wheat and rapeseed cake to determine which of the 4 phytases was most suitable under rumen-like conditions. The feedstuffs were incubated with a mixture of physiological buffer, ruminal fluid, and exogenous phytase at pH 6.2, after which the samples were incubated for different periods. Incubations were stopped using HCl, and the samples were analyzed for inositol phosphates via high performance ion chromatography. Addition of phytase (Phy1) resulted in enhanced degradation of myo-inositol hexakisphosphate (InsP6) in rapeseed cake, whereas addition of exogenous phytase did not improve the degradation of InsP6 in wheat. Only rapeseed cake was therefore used subsequently. All 4 phytases increased degradation of InsP6 in rapeseed cake in the in vitro system, and degradability of InsP6 increased with higher incubation time and higher phytase dosages, independent of phytase. Addition of 2 units of phytase per gram of substrate of the phytases Phy1, Phy2, Phy3, and Phy4 led to an undegraded InsP6 content of 56, 49, 70, and 18%, respectively, when incubated with rapeseed cake for 6 h, indicating that Phy2 and Phy4 were the most effective phytases. However, Phy2 had a higher specific activity than Phy4, as 60% of the original InsP6 content was remaining after 3 h when 5 mg of enzyme protein per gram of substrate of Phy2 was added to rapeseed cake, whereas 150 mg of enzyme protein per gram of substrate of Phy4 was necessary to achieve a similar result. Therefore, Phy2 appeared to be most applicable under rumen-like conditions.