In a study with 32 growing–finishing crossbred gilts (26–109 kg BW) the effects of benzoic acid and phytase (Peniophora lycii) on nutrient digestibility in P reduced diets was examined. All animals were restrictively fed one of four experimental diets: control diet (CC) without any supplementation, control diet with 0.5% benzoic acid (CB), phytase diet (750 IU/kg,) without benzoic acid (PhyC) and phytase diet with 0.5% benzoic acid (PhyB). Total P (digestible P) content of the control diets was 4 g/kg (1.43 g/kg). In the grower period a negative interaction of benzoic acid×phytase on apparent crude protein and energy digestibility was observed. In the finisher period both additives increased digestibility of P by 12%. Phytase improved Ca digestibility in both fattening periods (+13%). In the finisher period an interaction of benzoic acid×phytase reduced Ca digestibility from 0.62 in diet PhyC to 0.54 in diet PhyB. The results of this study indicate that the combination of benzoic acid and phytase in P reduced diets can adversely affect apparent nutrient and mineral digestibility. So far, the underlying mechanisms remain unclear.

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