Supranutritional phytase and dietary phosphorus effects on White Leghorns: I. Performance and egg traits.

This study evaluated the effects of supranutritional phytase supplementation (4,000 FYT/kg) in feeds having varying dietary phosphorus (P) on performance, egg traits, and ileal digestibility of White Leghorns (Bovans White) hens from 26 to 57 wk of age. A total of 324 hens were assigned to a 2 × 6 factorial: feeds with or without phytase vs. six graded increases of dietary P (avP = 0.09 to 0.44 % equivalent to 0.07 to 0.31 % digestible P). Responses were evaluated over eight 28 d periods; ileal digestibility was determined at the end of the trial. Significant phytase × avP interactions were observed for BW gain (BWG), feed conversion ratio (FCR; kg/kg egg), egg production, and the digestibility of DM, energy, and CP (P < 0.05). Without phytase, BWG increased linearly with increasing avP, whereas FCR (kg/kg) and egg production showed quadratic responses, with optimum values at 0.33 and 0.37 % avP, respectively. In phytase-supplemented hens, BWG, FCR (kg/kg egg), egg production, and energy digestibility responded linearly, whereas DM and CP digestibility showed quadratic responses. Phytase supplementation increased BWG (+16.3 %), feed intake (FI; +1.7 %), egg production (+2.0 %), total eggs (+4 eggs/hen), egg weight (+0.5 g), eggshell proportion (+0.19 %), shell breaking strength (+0.17 kgf), shell thickness (+6 μm), and ileal P digestibility (+23.6 %), while improving FCR (kg/kg) and reducing yolk percentage (P < 0.05). Independently of phytase, FI, eggshell proportion, and shell thickness increased linearly with increasing avP, whereas egg weight was maximized at 0.30 % avP. Feed conversion ratio (kg feed/dozen eggs) responded quadratically to avP, with an estimated optimum at 0.34 % avP. Calcium digestibility decreased linearly as avP increased, whereas P digestibility was unaffected by avP (P > 0.05). In conclusion, supranutritional phytase supplementation modified the response of laying hens to dietary P, reducing the avP concentration required to sustain productive performance from 0.33 to 0.37 % to 0.23-0.27 %.