An experiment was conducted to evaluate the influence of a novel microbial phytase on performance, tibia ash, and the content of phytate, phytate esters, and inositol in the gizzard of young broilers. Male Cobb 500 broilers (n = 1,680) were fed 1 of 7 experimental diets: positive control (PC) formulated to meet or exceed nutrient recommendations; PC plus dicalcium phosphate (PC+DCP) formulated to provide Ca and P at 0.10% above the PC; PC plus 500 U/kg of microbial phytase (PC+500); negative control (NC) with Ca and P reduced from the PC by 0.16% and 0.15%, respectively; and the NC plus phytase at 500 (NC+500), 1,000 (NC+1,000), or 1,500 (NC+1,500) U/kg. Diets were fed in crumbled form to 20 birds/pen and 12 replicate pens/diet from d 0 to 21. On d 21, 4 birds/pen were euthanized for collection of right tibias and gizzard digesta for determination of tibia ash and gizzard phytate. In general, broilers fed the NC diet had reduced (P ≤ 0.05) feed intake and BW gain compared with broilers fed diets supplemented with phytase, but not different than the PC or PC+DCP. Phytase supplementation in the NC diet improved (P ≤ 0.05) BW gain comparable with or above that of the PC. Feed conversion ratio was improved in broilers fed the NC+1,000 or NC+1,500 compared with broilers fed all other diets. Tibia ash was reduced (P ≤ 0.05) in broilers fed the NC compared with broilers fed all other diets, and phytase supplementation improved tibia ash comparable with the PC. Phytase supplementation reduced (P ≤ 0.05) phytate (inositol hexa-phosphate) concentration in the gizzard. Inositol concentration in the gizzard was higher (P ≤ 0.05) in birds fed NC+1,000 or NC+1,500 compared with all other diets and this was correlated with growth performance (P ≤ 0.05) rather than tibia ash (P > 0.05). Improvements in feed conversion ratio associated with superdoses of phytase may be attributed to phytate destruction and the provision of inositol.
Keywords: broiler; feed efficiency; inositol; phytase; phytate.