Intrinsic phytase and the limits of available phosphorus values for poultry

Phosphorus nutrition in poultry is guided by tables — for example, NRC (NASEM), INRA (Feedipedia, Feedtables) — that list total and available phosphorus for common feed ingredients. These values are essential for formulation, but they can sometimes mislead. Why? Because available phosphorus (AvP) values are not fixed constants. They depend heavily on the presence — and survival — of intrinsic phytase in cereals. When diets are heat-treated, those assumptions can fall apart.

The “available phosphorus” numbers in nutrient tables are mostly derived from animal trials. If wheat looks like it has more available phosphorus than corn, that’s because its intrinsic phytase was active during those trials, liberating phosphorus from phytate.