METABOLISM AND NUTRITION The Effects of Dietary Available Phosphorus Levels and Phytase on Performance of Young and Older Laying Hens

ABSTRACT In the first of two experiments (20 to 70 wk of age), eight treatments consisted of corn-soybean meal diets (0.34 % total P, 3.8 % Ca, 17 % CP, 2,758 kcal 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 diet. A second experiment evaluated the effect of feeding the 0.10 % AP diet with and without phytase on performance and time required for onset of P deficiency in older hens (70 to 76 wk of age). In Experiment 1, the 0.10 % AP diet with no supplemental phytase depressed performance by 28 wk of age. No other significant differences in performance were observed among treatments for the entire 20- to 70-wk period ex-cept that the 0.15 % AP diet with no phytase resulted in body weights and tibia ash that were lower (P < 0.05) than those of hens fed the 0.45 % AP diet during the last (Key words: available phosphorus, phytase, layer