Increased plasma inositol in response to high levels of phytase supplementation is more related to increased dietary phytate phosphorus rather than total phosphorus utilization
A total of 768 broilers were used to study the influence of phytase supplementation in broilers reared on new or old litters and receiving diets with low or high levels of available P (aP). The litter from a previous experiment was used as a source of mild challenge to the birds. The birds were allocated at 1 d old to 12 treatments in a 2 × 2 × 3 factorial arrangement with 2 levels of aP (0.3%, negative control or NC; and 0.45%, positive control or PC), 2 types of litter (new or old) and 3 levels of phytase (0, 1,000, and 2,000 FYT/kg). Excreta were collected from birds on d 19 and 20 and ileal digesta were collected on d 21. Blood was collected from one representative bird per pen; plasma was separated out by centrifugation and the plasma was used for inositol measurement. Diets, ileal digesta and excreta were analyzed for Ti, total P, and phytate P (PP). Three-way interaction was only significant for ileal PP disappearance with phytase promoting greatest (P < 0.01) PP disappearance in birds reared on new litter and receiving NC diet. There was significant (P < 0.05) control × phytase interaction for ileal P and total-tract P utilization and ileal PP disappearance with phytase increasing (P < 0.05) ileal PP disappearance and P utilization only at 2,000 FYT/kg in PC diet but at both 1000 and 2000 FYT/kg in NC diets. Phytase increased (P < 0.01) total-tract PP disappearance in both PC and NC diets but PP disappearance at 2,000 FYT/kg was 10% points greater in NC compared with PC diets. Plasma inositol content increased (P < 0.01) stepwise with phytase supplementation but there were no other treatment effect on plasma inositol response. Plasma inositol was highly correlated (P < 0.01) with ileal (r = 0.89) and total-tract PP (r = 0.91) disappearance; less with ileal P (r = 0.77) but not with total-tract P (r = 0.26) utilization. It was concluded that the increased plasma inositol content in response to high supplemental levels of phytase is more related to dietary PP rather than total P utilization and this response may partly explain some of the extra-phosphoric effects of phytase.
Other Titles/Title of Conference
Poultry Science Association Meeting, Corpus Christi, USA