Phosphorus equivalency of exogenous phytase relative to phosphorus in monosodium phosphate in broiler chickens

The objective of this study was to estimate phosphorus (P) equivalency of exogenous phytase relative to P from monosodium phosphate (MSP) in broiler chickens. To attain this objective, the impact of dietary MSP or exogenous phytase on growth performance, ileal digestibility of P, and bone characteristics in broiler chickens was assessed. Six experimental diets consisting of a P-deficient basal diet based on corn and soybean meal, basal diet plus 0.9 or 1.8 g/kg of inorganic P from MSP, and basal diet plus 500, 1,000, or 2,000 FYT/kg of exogenous phytase. Calcium to P ratio in all diets was maintained at 1.5:1. A total of 576 male broiler chickens (Cobb 500; initial BW = 190 ± 17 g) on d 8 post hatching were allotted to the 6 dietary treatments in a randomized complete block design using BW as a blocking factor. Each dietary treatment contained 8 replicate cages with 12 birds per cage. On d 11 post hatching, 7 birds from each cage were euthanized by CO₂ asphyxiation and dissected for the collection of ileal digesta. On d 18, ileal digesta were also collected from the remaining 5 birds in each cage. The left femur and tibia were collected from the bird with the median BW on d 11 and 18 from each cage, and analyzed for bone breaking strength and bone ash. Weight gain and gain-to-feed ratio linearly or quadratically increased (P < 0.05) in every period as the inclusion rate of MSP or phytase increased. Ileal digestibility of P linearly increased (P < 0.05) on d 11 with increasing MSP, but there was no significant effect on d 18. Increasing phytase concentration linearly increased (P < 0.05) ileal digestibility of P on d 11 and 18. Increasing dietary MSP or phytase linearly increased ileal digestible P concentration in diets (P < 0.05). Bone breaking strength and bone ash linearly or quadratically increased (P < 0.05) with increasing inclusion rate of MSP or phytase on d 11 and 18. The equivalency of 1,000 FYT/kg of exogenous phytase based on dietary ileal digestible P concentration was 1.5 and 1.2 g/kg of inorganic P in diets on d 11 and 18, respectively. The current results showed that the supplementation of MSP or exogenous phytase can increase growth performance, ileal P digestibility, bone breaking strength, and bone ash in young broiler chickens.