Effect of Exogenous Phytase on the Phosphorus and Zinc Metabolism of Fattening Bulls

This study investigated the effects of exogenous phytase, different dietary phosphorus (P) and zinc (Zn) levels on the P- and Zn-metabolism of fattening bulls. 48 German Holstein bulls (average initial live weight 312 ± 49 kg) were used for a feeding trial and allocated to four dietary treatments, P/Zn, P+MIN/Zn, P/Zn+PHY and P/Zn+MIN. All bulls received a diet of 80 % corn silage and 20% concentrate on a dry matter (DM) basis. The corn silage intake was for ad libitum and the concentrate intake restricted. The concentrate of P+MIN/Zn was supplemented with dicalcium phosphate. The concentrate of the P/Zn+PHY group was supplemented with an exogenous phytase (0.1 g/kg DM in the diet, 50 000 FTU/g) and the concentrate of the P/Zn+MIN group was supplemented with Zn. The P- and Zn-concentration in the diet of the P/Zn-, P+MIN/Zn-, P/Zn+PHY- and P/Zn+MIN-groups were 2.41, 2.99, 2.48 and 2.41 g P/kg DM and 33.2, 33.6, 34.0 and 38.8 mg Zn/kg DM, respectively. No differences in P- and Zn-concentration of faeces, liver, testes and performance were observed between the treatments. In the Os metacarpale, P- and phytase supplementation resulted in a slightly higher P-concentration, while the Zn addition led to the lowest value (P=0.062). Overall, it becomes clear that the microbial phytase of the rumen is sufficient enough to make the indigestible phytate-P and the hardly digestible Zn digestible for ruminants. The supplemented dietary phytase has no influence on the bioavailability of the mineral P and the trace element Zn.