ABSTRACT
The ruminal disappearance of phytate phosphorus (InsP6 -P) from maize grain and rapeseed meal (RSM) was determined in two in vitro studies. In experiment 1, two diets differing in phosphorus (P) and InsP6 -P concentration were fed to the donor animals of rumen fluid (diet HP: 0.49% P in dry matter, diet LP: 0.29% P). Maize grain and RSM were incubated in a rumen fluid/saliva mixture for 3, 6, 12 and 24 h. In experiment 2, a diet similar to diet HP was fed, and the rumen fluid was mixed with artificial saliva containing 120 mg inorganic P/l (Pi) or no inorganic P (P0). Maize grain and RSM were incubated with either buffer for 3, 6, 12 and 24 h. Total P (tP) and InsP6 concentration were analysed in the fermenter fluids and feed residues. The disappearance of InsP6 -P from maize was completed after 12 h of incubation in both experiments. From RSM, 93% (diet LP) and 99% (diet HP) of the InsP6 -P in experiment 1 and 80% (Pi) and 89% (P0) in experiment 2 had disappeared after 24 h of incubation. InsP6 -P disappearance was higher when diet HP was fed (maize: 3 and 6 h; RSM: 6 and 24 h of incubation) and when rumen fluid was mixed with buffer P0 (maize: 6 h; RSM: 12 and 24 h of incubation). InsP6 -P concentration in the fermenter fluids was higher for maize, but no accumulation of InsP6 -P occurred, indicating a prompt degradation of soluble InsP6 . These results confirmed the capability of rumen micro-organisms to efficiently degrade InsP6 . However, differences between the feedstuffs and diet composition as well as the presence of inorganic P in the in vitro system influenced the degradation process. Further studies are required to understand how these factors affect InsP6 degradation and their respective relevance in vivo.
