Studies on the effects of microbial phytase on amino acid digestibility and energy metabolisability in caecectomised laying hens and the interaction with the dietary phosphorus level

Abstract

1. Caecectomised laying hens were used in two assays to study the effects of a microbial 6-phytase on amino acid (AA) digestibility and energy metabolisability using (1) diets with phytate-rich protein sources and (2) with two dietary phosphorus (P) levels. The two assays followed a 2 × 2-factorial arrangement of treatments using 8 hens per treatment. The hens were housed individually in metabolism cages, and excreta were quantitatively collected for a period of 5 d. 2. In Assay 1, two dietary P levels (8.0 and 4.0 g/kg dry matter) and two levels of phytase supplementation (0 and 1000 U/kg diet) were used in diets that were mainly based on maize, sunflower meal and wheat gluten. The digestibility of AA was 0⋅01 to 0⋅02 lower in the diet with the low P than with the high P concentration. The effect of P content was significant for 12 out of the 14 AA studied. The supplementation of phytase significantly improved the degradation of myo-inositol(1,2,3,4,5,6)hexakisphosphate (IP6), but affected neither AA digestibility nor energy metabolisability. An interaction between the two factors was not detected. 3. In Assay 2, diets contained one main protein source (sunflower meal or rapeseed meal) at a concentration of 250 g/kg. The diets were either supplemented or not with phytase (1500 U/kg diet). On average, AA digestibility was 0·01 lower in the rapeseed meal-containing diet than in the sunflower meal-containing one. The maximum difference was 0·03. The effect of the protein source was significant for 9 of the 14 AA studied. The supplementation of phytase had no significant effect on AA digestibility or energy metabolisability. 4. Our studies do not substantiate the hypothesis that improved IP6 degradation due to phytase supplementation is associated with improved AA digestibility and energy metabolisability in laying hens. An interaction between phytase efficacy to improve AA digestibility or energy metabolisability and the P level in the diet does not seem to exist.