Total tract retention and phytate hydrolysis in broiler diets deficient in available P and calcium with phytase
Three hundred eighty-four Ross 308 broilers were allocated to 6 dietary treatments for 21 d. Diets were a nutritionally adequate positive control (PC) and a negative control diet (NC; deficient in aP by 0.15% and Ca by 0.16%, relative to the PC) with each diet supplemented with 0, 500 or 1,500 FTU/kg phytase, creating a 2 × 3 factorial design. There were 8 replicates per diet with 8 birds per replicate. Excreta were collected on d 19–20 for determination of nutrient retention (TTR) and phytate hydrolysis. Gizzard digesta was collected on d 21 for measurement of phytate hydrolysis. Data were analyzed using JMP Pro 11 and means separated using orthogonal contrasts. Phytase supplementation increased DM (linear, P = 0.001), N (linear, P < 0.001), and P (quadratic, P = 0.017) retention, but only when supplemented in the NC diets (phytase × aP interaction, P < 0.02). Calcium retention decreased (P = 0.006) from 54 to 47% as aP increased in the diet. Phytase decreased (quadratic, P < 0.001) gizzard iP6 and iP5 content and increased (linear, P < 0.001) inositol content. Gizzard iP4 content increased (quadratic, P < 0.001) as phytase supplementation increased in birds fed the NC diet. There was no effect of phytase on gizzard iP4 in birds fed the PC (phytase × aP, P = 0.004). Excreta iP3, iP5, and iP6 decreased (quadratic, P < 0.01) and iP4 increased (linear, P < 0.01) in birds fed phytase in the PC. However, iP3 and iP4 increased (linear, P < 0.01) and iP5 and iP6 decreased (quadratic, P < 0.01) in birds fed the NC diet (phytase × aP interactions, P < 0.05). Excreta inositol content decreased (P < 0.001) in birds fed the PC compared with birds fed the NC. Phytase supplementation linearly increased (P < 0.001) inositol content in the excreta. The results show that phytate hydrolysis begins in the gizzard and significant iP3 and iP4 hydrolysis occurs in the latter parts of the gastrointestinal tract.
Other Titles/Title of Conference
Poultry Science Association Meeting, Louisville, Kentucky, USA