Abstract: An experiment was conducted to determine the effect of high doses of microbial phytase supplementation in corn-soybean meal diets on growth performance and serum biochemical indices. A total of 576 one-day old male Arbor Acres broilers were assigned to 6 dietary treatments,consisting of 8 pens of 12 birds each,and were fed two periods experimental diets from 1 to 21 d and 22 to 42 d. The diets include a positive control(0.69% TP,0.45% nonphytate P for 1 to 21 d;0.59% TP,0.35% nonphytate P for 22 to 42 d)and a negative control(0.60% TP,0.35% nonphytate P for 1 to 21 d;0.49% TP,0.25% nonphytate P for 22 to 42 d),and 4 more negative diets with 500,2000,8000,32000 FTU/kg phytase. The results showed that①High doses of phytase addition had significantly improved the ADG at 3 weeks(P＜0.05),while the feed intake and F∶G had no significantly differences(P＞0.05).②High doses of phytase addition had significantly improved the ADG and F∶G at 6 weeks( P＜0.05),with the phytase levels increasing,the ADG and F∶G had significantly increased( P＜0.05),the feed intake had no differences(P＞0.05).③Compared with the negative control diet with 8000 FTU/kg phytase improved the best performance ADG and F∶G. ④Diets with high doses of phytase had significant effect on serum P and Ca and Alkalescence(at 21 or 42 d). With the phytase levels increasing,the levels of serum P were significantly increased(P＜0.05),serum Ca were decreased,serum AKP were significantly decreased(P＜0.05).Therefore, graded doses and high doses of phytase supplementation beyond present standards(500 FTU/kg)could further improve growth performance and reduce serum AKP of broilers .

Key words: high doses; phytase; broiler; growth performance; serum biochemical parameters