The effects of dietary available phosphorus levels and phytase on performance of young and older laying hens

In the first of two experiments (20 to 70 wk of age), eight treatments cons isted of corn-soybean meal diets (0.34% total P, 3.8% Ca, 17% CP, 2,758 kca l ME/kg) containing 0.10, 0.15, 0.20, 0.25, or 0.45% available P (AP), with the three lowest AP diets supplemented with 300 units of phytase/kg of die t. A second experiment evaluated the effect of feeding the 0.10% AP diet wi th and without phytase on performance and time required for onset of P defi ciency in older hens (70 to 76 wk of age). Ln Experiment 1, the 0.10% AP di et with no supplemental phytase depressed performance by 28 wk of age. No o ther significant differences in performance were observed among treatments for the entire 20- to 70-wk period except that the 0.15% AP diet with no ph ytase resulted in body weights and tibia ash that were lower (P < 0.05) tha n those of hens fed the 0.45% AP diet during the last 30 wk. The mean daily AP intake of hens fed the 0.10% AP, 0.15% AP, 0.45% AP, or 0.10% AP + phyt ase diets was 94, 159, 499, or 108 mg, respectively. Excreta P concentratio n was decreased by approximately 50% in birds consuming 0.10% AP + 300 U/kg phytase compared with those consuming 0.45% AP. In the second experiment, P deficiency signs occurred within 3 wk of consuming the unsupplemented cor n-soybean meal diet (0.10% AP) compared with 8 wk in Experiment 1. The resu lts of this study indicate that phytase improves P utilization in corn-soyb ean meal diets for laying hens and that a corn-soybean meal diet containing 0.15% AP (159 mg AP/d) or containing 0.10% AP + 300 units of phytase/kg (1 08 mg AP/d) supported optimal egg production from 20 to 70 wk of age. Addit ionally, results suggested that older hens may exhibit P deficiency symptom s sooner than younger hens.