Recent findings regarding calcium and phytase in poultry nutrition

Abstract

Calcium (Ca) is an essential element for poultry and even a mild deficiency can lead to significant welfare and performance issues. As a result, it is often fed at levels in excess of requirement, partly as an insurance policy and, to some degree, because of its relatively low cost compared with other feed ingredients. However, when diets meet but do not exceed the phosphorus (P) requirements of the bird, a marginal Ca excess can interfere with P digestibility. This problem is exacerbated when phytases are used to provide some of the required P because Ca decreases the efficiency of phytate (IP6) hydrolysis in a dose-dependent manner. More recently, phytases have been used at very high doses (1500 FyTase units (FTU); ‘superdosing’) in commercial diets, to improve bird performance by removing as much of the dietary IP6 and lower esters of phytate (IP5, IP4, IP3 and IP2) as possible, all of which are considered anti-nutrients, and concomitantly producing as much inositol, a nutrient, as possible. In such a regimen, the ability of the phytase to degrade the lower phytate esters, namely IP4, IP3 and IP2, takes on greater importance than does simply releasing phytate P. Calcium has recently been shown to reduce the efficacy of hydrolysis of the lower phytate esters to a greater degree than the extent to which it decreases IP6 hydrolysis. As a result, Ca concentrations in the diet should be monitored frequently if the maximum value of a phytase is to be realised.