Phosphorus Digestibility by a Recently Isolated Phytase

Phytase supplementation of broiler diets can improve energy, amino acid, calcium (Ca) and phosphorus (P) utilization. Both fungal- and bacterial-derived phytases are commonly added to broiler diets. Phytases from different sources and even from the same source can have different pH optima, heat stability, and catalytic properties (Dersjant-Li et al, 2015). Furthermore, when different microbial phytases are included in diets, their efficacy in vivo can vary in comparison to their assayed activity. Therefore, biological efficacy can only be determined by feeding studies. New phytase products are constantly being developed and the efficacy of a phytase, recently isolated from E. coli, was examined.

Male Ross 308 broilers were randomly allocated into 20 cages (7 birds /cage) at 23 days post-hatch and offered a sorghum (920 g/kg) bioassay diet with celite (20 g/kg) as acid-insoluble ash (AIA) that was used as indigestible marker. The four dietary phytase treatments were: Diet1 (0 phytase units (FTU)/kg), Diet 2 (500 FTU/kg), Diet 3 (1000 FTU/kg) and Diet 4 (2500 FTU/kg). Each dietary treatment was fed as mash to 5 cages. After five days, lower ileal samples were collected and pooled for each pen. AIA and P in samples were determined using the method described by Huang (2004) and Plumstead et al (2008). Apparent ileal P digestibility were calculated by using equation described by Plumstead et al. (2008).

The birds fed diets containing phytase has higher apparent ileum P digestibility (P < 0.01) than the control group (46%). Apparent ileum P digestibility of Diet 2 and 3 increased to a similar amount (~ 61%). However, phytase superdosing in diet 4 increased (P< .0.01) apparent ileum P digestibility (77%) substantially.

The standard application of phytase is normally around 500 FTU/kg. It is not clear from the literature what constitutes superdosing but applications at least 3x the standard are referred to as superdosing. In this study, 5x the standard was used and digestibility of P was significantly increased. This study demonstrates that this phytase survives the acidic conditions of the gut and other studies indicate it also survives pelleting. These characteristics and its performance in vivo make it a possible commercial candidate.