ABSTRACT
There is a large body of scientific literature on this subject dating back over 30 years. Thousands of papers have been published on this subject in numerous journals since the mid-1980s, although as indicated by Angel and Sorbara (2014) a high proportion of papers have been lacking information on the content of phytate, phytase levels, their interaction and thus phytase efficacy. In some published studies, however, phytate phosphorus (P) has been analysed and its digestibility, either at the ileal or excreta level, have been determined. Increased P digestibility and utilization and, hence, reduced P excretion into the environment as a result of phytase addition to poultry diets have been demonstrated (Applegate et al., 2003; Penn et al., 2004; Angel et al., 2006; Leytem et al., 2007). The results of several phytate P digestibility studies, however, have shown that the liberation of P from phytic acid by phytase is incomplete, and as illustrated in Fig. 1, averages only 54% of phytate P hydrolysis of what is present in the diet (i.e. 0.15 vs. 0.28%). It must be emphasized, however, that the degree of phytate P release is not entirely due to microbial phytase supplementation but also a consequence of the endogenous intestinal mucosa phytase action (Maenz and Classen, 1998; McCuaig et al., 1972) and, potentially, the intrinsic phytase activity of feed ingredients. Both sources of phytase could contribute to a significant release of phytate P, which, as illustrated in Fig. 1, would average 0.07% of the diet. If this is taken into account, then the liberation of P from phytic acid following microbial phytase supplementation would average only 21% of phytate P (i.e., 0.07 vs. 0.28%). This does not account for the 0.1% reduction in available P content commonly used for phytase-supplemented poultry diets.
