EFFECTS OF SUPPLEMENTAL PHYTASE AND PHOSPHORUS ON HISTOLOGICAL, MECHANICAL AND CHEMICAL TRAITS OF TIBIA AND PERFORMANCE OF TURKEYS FED ON SOYBEAN-MEAL-BASED SEMI-PURIFIED DIETS HIGH IN PHYTATE PHOSPHORUS

Tibial traits were investigated for turkey poults fed on soyabean-meal -based semi-purified diets high in phytate P (2.2 g/kg) with added phy tase and inorganic P. Dietary treatments were: (1) 2.7 g non-phytate P (nP)/kg; (2) diet 1 + 1000 U phytase/kg diet; (3) 3.6 g nP/kg; (4) di et 3 + 800 U phytase; (5) 4.5 g nP/kg; (6) diet 5 + 600 U phytase; (7) 6.0 g nP/kg, Added phytase and nP increased (P < 0.006) tibial dry ma tter, ash weight and content, body-weight gain, feed intake and gain:f eed, The Mg and Zn concentrations in the tibial ash were also increase d (P < 0.001 and P < 0.09 respectively) by added phytase or nP; tibial P and Ca concentrations tended to be increased. Hypertrophy zone widt h of the tibial proximal end decreased (P < 0.001), while proliferatin g zone width, tibial length, and widths at the long and short axes inc reased (P < 0.003) as phytase and nP were added, The addition of phyta se also tended to enlarge the cartilaginous zone width, which was line arly increased (P < 0.05) by added nP, Disorganization scores of the h ypertrophy zone and trabecular bone were low, approaching normal (P < 0.05), for turkey poults fed on diets with phytase supplementation, an d tibial abnormality scores were Linearly decreased (P < 0.001) as nP levels increased (zero score is considered normal), Adding phytase and nP improved the orderliness of development, mineralization and arrang ement of cartilage and bone cells, and alleviated the effects of P def iciency on the histological and gross structure of the tibias, Tibial shear stress increased (P < 0.04) as phytase and nP a ere added, In su mmary, similar improvements in bone characteristics were achieved for turkey poults fed on a P-deficient diet supplemented with either phyta se or nP.