Phytase, citric acid, and 1α-hydroxycholecalciferol improve phytate phosphorus utilization in chicks fed a corn-soybean meal diet

Previous research from our laboratory has shown that phytase, citric acid, and 1α-hydroxycholecalciferol [1α-(OH) D₃] individually improve phytate P use in young chicks fed a P-deficient corn-soybean meal (C-SBM) diet. The current study was conducted to evaluate combinations of these additives on phytate P utilization. In 3 chick experiments, male crossbred chicks (New Hampshire x Columbian) were fed experimental diets from 8 to 21 d of age. The C-SBM basal diet used in all assays contained no supplemental P and was calculated to provide 23% CP, 0.13% nonphytate P (0.39% total P), 0.62% Ca, 25 mg of cholecalciferol/kg, and 3,260 kcal of TME/kg. In all 3 experiments, factorial arrangements (2 x 2 or 2 x 2 x 2) were used to evaluate 2 levels of phytase (0 and 300 units/kg), citric acid (0 and 3 or 4%), and 1α-(OH) D₃ (0 and 5, 10, or 15 μg/kg). Phytase, citric acid, and 1α-(OH) D₃ each increased weight gain and tibia ash in all 3 experiments. There were some significant interactions among the compounds, but these were not consistent across experiments. Using standard curve methodology for tibia ash data, it was estimated that 0.03, 0.02, and 0.04% P were released by 3% citric acid, 300 units of phytase/kg, and 5 μg 1α-(OH) D ₃/kg, respectively, and that the combination of all 3 compounds resulted in the release of 0.13% P. Our results indicate that all 3 compounds increased phytate P use, and that their effects were generally additive, with some possible synergism between citric acid and 1α-(OH) D₃.