The efficacy of 2 phytases on inositol phosphate degradation in different segments of the gastrointestinal tract, calcium and phosphorus digestibility, and bone quality of broilers

Abstract

The anti-nutritional effects of dietary inositol phosphates (IP6 through IP3) have been recognized in broiler chickens; however, inositol hexaphosphate (IP6) is more potent than the lower IP esters. The efficacies of 2 commercial phytases, a Buttiauxella sp. phytase (BSP) and a Citrobacter braakii phytase (CBP) at 500 and 1,000 FTU/kg, were studied on IP6-3 concentrations in the crop, proventriculus + gizzard, and distal ileum digesta, and ileal IP6 disappearance in broilers at day 22. Apparent ileal P and Ca digestibility, and bone quality at days 22 and 33 were also measured. Female Ross 308 broilers (n = 1,890; 30 birds × 7 diets × 9 replicates) were fed corn-soy-based crumbled diets. The 7 diets included a primary breeder recommendation-based positive control diet (PC); the PC marginally reduced in available P by 0.146% and Ca by 0.134% of the diet, (NC1) or moderately reduced by 0.174 and 0.159% of the diet, respectively (NC2). Other diets were the NC1 + BSP or CBP at 500 FTU/kg (NC1+500BSP and NC1+500CBP) and the NC2 + BSP or CBP at 1,000 FTU/kg (NC2+1,000BSP and NC2+1,000CBP). Each of the NC1 and NC2 had distal ileum IP6 disappearance similar to that of PC, but each had lower P digestibility and the majority of measured bone quality parameters than the PC. The ileal IP6 levels were decreased by 52.0 and 32.7% for NC1+500BSP and NC1+500CBP, respectively, relative to NC1 and by 73.6 and 50.9% for NC2+1,000BSP and NC2+1,000CBP, respectively, relative to NC2 (P < 0.001), with a similar effect for distal ileum IP6 disappearance. Overall, phytase in the NC diets increased P digestibility, and femur breaking strength and cortical bone mineral density at days 22 and 33. Overall, each of the phytases at each dose degraded IP6-3 across the gastrointestinal tract segments to increase P digestibility and the P and Ca utilization in bone. However, dietary BSP at 1,000 FTU/kg was most effective. Supplemental phytase degrades phytate to decrease the anti-nutritional effects in a dose- and phytase-dependent manner.

Keywords: bone; broiler chicken; gastrointestinal tract; phytase; phytate.