The effect of phosphorus, phytase enzyme, and calcium on the performance of layers fed corn-based diets

An experiment employing a factorial arrangement of two levels of Ca, two levels of available P (AP), and three levels of phytase enzyme was carried out with 360 ISA White layers from 18 to 67 wk of age. The Ca levels were maintained at 3.7 and 4.0% throughout the experiment. The AP levels were 0.2 and 0.4% for the high and low treatments until 55 wk of age and were reduced to 0.11 and 0.22% thereafter. Phytase enzyme levels were 0, 250, and 500 phytase units (FTU)/kg of feed. In the period before Week 55, either level of AP was likely adequate for maximum production. However, when lower levels of AP were fed after this time, low AP was associated with reduced BW and egg production, and enzyme supplementation was able to compensate for low AP. In this period, high AP and the highest level of phytase produced negative effects on BW, egg weight, and the feed conversion ratio. The ratio of Ca to AP was important; shell quality was best with high or low levels of both. With high levels of Ca, enzyme supplementation compensated for low levels of AP and overcompensated with a high level of AP. These effects were reduced or absent with low levels of Ca. It is clear from this study that phytase enzyme can compensate for low levels of AP in diets based on corn and soybean meal, but that the optimum level of supplementation depends as well on the Ca level.