Effect of high phytase levels on growth performance and calcium and phosphorus metabolism in broilers fed a non-inorganic phosphorus diet.

The effects of high phytase levels on growth performance and calcium (Ca) and phosphorus (P) metabolism in broilers fed non-inorganic P diets were investigated. A total of 600 one-day-old broilers were assigned to either a control diet or a non-inorganic P diet supplemented with one of two commercial phytases (P1 and P2) at 1,000 (NP, normal level of phytase) or 10,000 FTU/kg (HP, high level of phytase). Compared with the control group, HP treatments had comparable feed intake, body weight gain and feed conversion ratio, whereas NP supplementation reduced the parameters, particularly during 22-42 and 1-42 days of age (p < 0.05). Both HP and NP treatments significantly increased apparent P retention during the finisher stage, compared with the control group (p < 0.01). At 42 days of age, compared with the control group, the HP chickens had higher tibial and femoral Ca contents (p < 0.01) and comparable P levels, whereas the NP chickens showed lower Ca and P contents (p < 0.01). High phytase levels increased blood concentrations of P and PTH, along with tibial and femoral lengths. Compared with the control group, phytase altered the expression of genes involved in Ca and P transport. NP treatment increased duodenal CaBP-D28k expression, while the P1 treatment at 1,000 FTU/kg significantly upregulated renal NPt2a and CaBP-D28k expression (p < 0.01). In conclusion, supplementation with 10,000 FTU/kg phytase to corn-soybean meal diet without inorganic P supplementation largely maintained growth performance and bone mineralization while improving P utilization and reducing P excretion. These findings indicate that 10,000 FTU/kg phytase can effectively replace inorganic P supplementation in broilers.