Iron bioavailability in soybean meal as affected by supplemental phytase and 1 alpha-hydroxycholecalciferol.

An Fe depletion-repletion chick bioassay was conducted to determine whether supplemental microbial phytase or 1 alpha-hydroxycholecalciferol (1 alpha-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), 1 alpha-OHD3 (10 micrograms/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+1 alpha-OHD3, and 29.2% for SBM+phytase+ 1 alpha-OHD3.