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The ability of commercial phytases to increase nutrient digestibility, performance, and bone ash content of broilers has been well studied. However, the effects of supplemental phytase in available P- (avP) and Ca-deficient diets depend on the ability of the enzyme to degrade phytate (inositol hexaphosphate; IP6) in the gastrointestinal tract (GIT). Commercially available phytases are from various bacterial or fungal sources. The efficacy of phytase supplementation in avP- and Ca-reduced diets to prevent bone loss to maintain bone ash, breaking strength, and mineral density across trabecular and cortical bone tissues is clear. However, there is no information on how source and dose of dietary phytase affect IP degradation in each segment of the GIT to affect cortical and trabecular bone densitometry in broilers. Therefore, the objective of this study was to assess the effects of 2 phytases at 500 or 1,000 FTU/kg on IP6–3 degradation in different GIT segments; P and Ca digestibility; and bone strength, ash, and density in broilers.
Female Ross 308 broilers (n = 1,890) were housed with 30 chicks in each of 63 wire-floored pullet cages. A total of 7 dietary treatments were each assigned to 9 replicate cages and were fed to the birds as crumbled starter (day 0 to 8), grower (day 9 to 22), and finisher (day 23 to 33) diets. The dietary treatments were a nutritionally adequate positive control diet (PC); the PC diet with avP and Ca marginally reduced by 0.146 and 0.134% of the diet, respectively (NC1), or moderately reduced by 0.174 and 0.159% of the diet, respectively (NC2). Other diets were the NC1 and NC2 diets supplemented with a Buttiauxella sp. phytase (BSP) and a Citrobacter braakii phytase (CBP) at 500 FTU/kg to the NC1 diets (NC1+500BSP and NC1+500CBP, respectively) and at 1,000 FTU/kg to the NC2 diets NC2+1,000BSP and NC2+1,000CBP. Celite was included in all diets at 2% as an indigestible marker. The 7 dietary treatments were randomly and evenly distributed across the 63 cages. At 8, 22, and 33 D of age, 14, 11, and 5 birds, respectively, from each cage were euthanized. The right femurs of 4 birds from each cage were excised for bone quality analysis (Bone breaking strength (BBS), bone ash content, bone densitometry). Bone cross-sectional areas (BCSA in mm2) and mineral density (BMD in mg/mm3) of total, cortical, and trabecular bone tissues were measured. The digesta from the distal half of the ileum were collected and pooled within the cage. The diets and the distal ileum samples were analyzed for acid insoluble ash (AIA). The apparent ileal digestibility of P (AIDP) and Ca (AIDCa) were determined based on the analyzed P and Ca levels and analyzed AIA in diet and digesta samples.
At 22 D of age, the NC1 and NC2 diets decreased mid-diaphysis and proximal-metaphysis cortical BMD relative to the PC group. At 500 FTU/kg, only BSP alleviated the adverse effects of NC1, but at 1,000 FTU/kg, both BSP and CBP alleviated the adverse effects of NC2 (P ≤ 0.001). The day 33 mid-diaphysis cortical BMD was decreased by NC1 and NC2 relative to PC, and each phytase alleviated the adverse effect of the NC1 and NC2 diets (P = 0.005). Proximal metaphysis cortical BMD was nearly significantly decreased (P = 0.096) by NC2 relative to the PC but was restored by supplementation of either phytase at 1,000 FTU/kg feed. The day 8 AIDP was maintained by NC1 but decreased by NC2 relative to PC and was increased by NC1+500BSP and NC1+500CBP relative to NC1 and PC (P < 0.001). Relative to NC2, each phytase increased AIDP. The day 22 and 33 AIDP were each decreased by NC1 and NC2 relative to PC and were alleviated by supplemented phytase regardless of type and dose. However, day 22 and 33 AIDP were each higher with BSP relative to CBP, regardless of dose (P < 0.001). The day 22 AIDCa was increased by NC1, maintained by NC2 compared to PC, and was increased by BSP and CBP at 1,000 FTU/kg. There were no treatment effects at day 8 and 33 (P < 0.001).Overall, distal ileum IP6–5 concentrations were decreased by the BSP relative to the CBP at both doses and by NC2+1,000BSP relative to NC1+500BSP. Also in the distal ileum, however, IP4 concentration was increased by NC1+500BSP relative to NC1+500CBP but similar at the 1,000 FTU/kg dose, and the IP3 concentration was increased in the NC2+1,000BSP compared to NC2+1,000CBP but similar at the 500 FTU/kg dose. Also, the distal ileum IP6 disappearance was maintained in the NC1 and NC2 diets relative to the PC and was increased by each respective phytase supplementation. Relative to the control diets, the distal ileum IP6 disappearance was also further increased by BSP relative to CBP at both doses and by 1,000 FTU/kg relative to 500 FTU/kg with both phytases.
To efficiently degrade and decrease the anti-nutritional effects of IP on nutrient digestibility and utilization, the source and dose of dietary phytase are essential factors to consider. Both BSP and CBP at 500 and 1,000 FTU/kg each decreased IP6 across the crop, proventriculus + gizzard, and distal ileum to increase P availability and bone quality traits relative to the non-phytase containing diets. However, BSP at 1,000 FTU/kg had the greatest effect on IP6–4 degradation across the digestive tract segments and increased P availability and bone quality. The poultry industry can effectively use phytase to reduce inorganic P supplementation, which could decrease feed cost and P excretion, without reducing bone quality in broilers.