Iron Bioavailability in Soybean Meal as Affected by Supplemental Phytase and 1α-Hydroxycholecalciferol

An Fe depletion-repletion chick bioassay was conducted to determine whether supplemental microbial phytase or 1α-hydroxycholecalciferol (1α-OH D₃) would improve the bioavailability of Fe in soybean meal (SBM). Weight gain, hemoglobin, and hematocrit were markedly improved when increasing levels (0, 10, 20, and 80 mg/kg) of Fe from analytical grade ferrous sulfate (FeSO₄·7H₂O) were added to the Fe-deficient casein-dextrose basal diet containing 20 mg Fe/kg. Addition of 19 mg Fe/kg from SBM to the basal diet improved (P < 0.05) hemoglobin and hematocrit, but the response was less than that obtained from 10 mg Fe/kg from FeSO₄·7H₂O. Phytase (1,430 units/kg), 1α-OHD₃ (10 μg/kg), or the combination, added to the SBM-fortified basal diet did not further improve hematocrit or hemoglobin, indicating that Fe bioavailability of SBM was not increased by either of these feed additives. Based on standard-curve methodology, and using hemoglobin as a criterion, the relative bioavailability of Fe was 38.5% for SBM, 21.0% for SBM + phytase, 23.2% for SBM + 1α-OHD₃, and 29.2% for SBM + phytase + 1α-OHD₃.