| An experiment was conducted to study phosphorus nutrition and effects of phytase supplementation in broilers fed different dietary levels of inorganic phosphorus on growth performance, bone growth, serum biochemical indicator, slaughter performance and nutrient utilization rate. A total of 1500 broilers were chosen and assigned randomly to five treatments. A diet of adequate inorganic phosphorus without phytase was used as control, and the other four calcium phosphate dibasic levels which were 75%, 50%, 25%, 0% of the control were performed with phytase addition, respectively. Dietary Ca: TP ratios between 1.2 to 1.4 were controlled in all treatments.The results demonstrated that ADG (63.7 g/d) of 50% calcium phosphate dibasic group was the highest and feed gain ratio (1.81) was the lowest in all groups. The results demonstrated that ADFI and ADG of no inorganic P group were 111.4 g/d and 56.7 g/d, which were significantly lower than the control (P <0.05) in the present experimental condition.Tibia fresh weight and fat-free rate were not significantly different in all treatments (P >0.05), and fat-free rate was increased in response to decreasing inorganic P levels; Tibia fat-free weight was decreased in response to decreasing inorganic P, and it was significantly lower than the other groups at 28d of the age (P <0.05). Tibia ash content in no inorganic P group was lower than the other groups at 28d of the age (P <0.05). Tibia Ca and P contents in no inorganic P group were lower than the other groups, but they did not differ significantly (P >0.05) among all treatments. Tibia Mg, Mn, Cu, Fe and Zn contents increased in response to decreasing dietary inorganic P at 28d of the age, Tibia Mg, Mn, Fe contents with phytase addition groups had the same variation at 42d of the age. Tibia breaking strength in no inorganic P group was lower than the other groups, and it was significantly lower than the other groups at 28d of the age (P <0.05).Serum inorganic P and calcium concentrations were not significantly different among treatments (P >0.05). Serum ALP activity of no inorganic P group was highest (2667.80 U/L) in all groups. Serum Cu and Zn contents were not significantly different among treatments (P >0.05).At 28d of the age, percentage of carcass yield, eviscerated yield and half-eviscerated yield of no inorganic P were significantly lower than the control (P <0.05), the breast and leg muscle percentage in all treatments were not significantly different (P >0.05). At 42d of age, the percentage of carcass yield, eviscerated yield, half-eviscerated yield, breast and leg muscle of all treatments were not significantly different (P >0.05).The NPU of all phytase addition groups were higher than the control group by 2.10%,4.95%,3.48%,5.66% with the decreasing inorganic P levels, but they were not significantly different among treatments (P >0.05). The treatment groups had the increasing tendency to the utilization rate of mineral elements in response to decreasing inorganic P levels. The phosphorus of phytase groups were lower than the control group by 11.0%, 17.9%, 23.9%, 28.4% with the deceasing inorganic P levels in excretion, and no inorganic P group was significantly different than the control group (P <0.05).The study indicated that the growth performance and utilization of the mineral elements were improved with phytase addition in diet, the fecal P excretion were reduced. The study indicated serum ALP activity was more sensitive in measurement dietary Ca and P nutrients than serum Ca and serum inorganic P. And the slaughter performance was not influenced with phytase addition in the decreasing dietary inorganic phosphorus levels. But phytase can not replace calcium phosphate dibasic completely. And 50% calcium phosphate dibasic group of the control (0-4W: Ca 0.76%, TP: 0.54%; 5-7W: Ca 0.70%, TP 0.53%) appeared to provide better efficacy. Respecting contribution of phytase on releasing binding minerals, it was necessary to reevaluate dietary requirements of mineral elements. |
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