Relationship between graded doses of three microbial phytases and digestible phosphorus in pigs

The efficacy of three microbial phytases to increase the amount of digestible phosphorus (dP) was studied in pigs. A basal diet was prepared meeting the requirements of 30-kg pigs with the exception of P. Concentrations (in g/kg dry matter) were: P 2.9, phytate P 1.3, calcium (Ca) 6.9, and crude protein 208. Intrinsic phytase activity was below detection limit. Microbial phytase was supplemented from three sources (Aspergillus niger (Asp), Peniophora lycii (Pen), and consensus phytase (Con)) at the following levels (phytase units (FTU) per kg diet) : 150, 300, 450, 600 and 900. Diets were pelleted without steam. Forty-eight male castrated crossbred pigs ((Large White 5 German Landrace) 5 Pietrain) initially weighing, on average, 28 kg were individually penned. Each of the 16 diets was offered to three pigs in three consecutive periods of 17 days each, resulting in nine replicates per treatment. No animal received the same diet twice. Faeces were spot-sampled for each individual pig twice daily for the last 7 days of each period. TiO2 was used as an indigestible marker. An exponential function was fitted to the data, and both marginal and cumulative efficacies of phytases were described on the basis of the resulting functions. No significant period effect was detected for any of the obtained data. On overall average, daily live-weight (LW) gain was 730 g, and 2.57 kg food were needed per kg LW gain. Neither criterion was significantly affected by source or level of supplementary phytase. Digestibility of organic matter and crude protein averaged 0.90 and 0.84, respectively, again without a significant treatment effect. Digestible P concentration in no case exceeded 1.5 g/kg DM, indicating that P supply to pigs was marginal in all treatments. Digestibility of P from the basal diet was 0.22. P digestibility was significantly affected (P = 0.001) both by the source and by the level of supplementary phytase. It responded in a non-linear fashion to increasing phytase supplementation, this course being less clear for Pen than for Asp and Con phytase. In no case was a clear plateau in P digestibility reached within the range studied. For Asp and Con, marginal efficacy decreased from about 2 mg dP per incremental FTU at low supplementary level to roughly 0.6 mg dP per incremental FTU. This clear dose dependent effect was not present for the Pen phytase, where about 0.6 to 0.7 mg dP per incremental FTU were released almost irrespective of the level of supplementation. It is concluded that phytases of different origin rank differently from each other regarding their efficacy, depending on the level of supplementation. Dose-response studies are recommended in cases where different phytases are to be compared.