Abstract:

Determination of precaecal digestibility of phosphorus (pcdP) has been put forward as the approach of choice to characterise the availability of phosphorus (P) from feed raw materials and mixed diets in poultry. Mixed diets usually contain P sources of plant and mineral or animal origin. In plant feed raw materials, pcdP is closely related to gastrointestinal degradation of phytate (any salt of phytic acid (myo-inositol 1,2,3,4,5,6-hexakis dihydrogen phosphate; InsP₆)). The broiler has the potential to hydrolyse two third of dietary InsP₆ in low-calcium (Ca) P diets devoid of any phytase. However, supplements of Ca or P or both strongly reduce gastro-intestinal InsP₆ hydrolysis and thus digestibility of InsP₆-P. These effects can be compensated by concurrent supplementation of phytase, with compensatory effects being higher at dosages exceeding the industry standard level of supplementation. The standard protocol for the determination of pcdP of the World’s Poultry Science Association contains limitations in regard to dietary P and Ca levels, but it does not consider interactions with InsP₆ hydrolysis. Thus, pcdP values of non-plant P sources are underestimated if determined in diets that contain InsP₆ and not corrected for InsP₆ disappearance. Likewise, pcdP values of plant P sources are overestimated in diets that contain non-plant P sources. It is suggested that chemical analysis in pcdP studies is extended by InsP₆ determination.