Zinc bioavailability in soybean meal

A phytate-containing soy protein concentrate (SPC) diet (13.5 mg Zn/kg) and a phytate-free egg white diet (.3 mg Zn/kg) were used to determine the rel ative bioavailability (RBV) of Zn in dehulled soybean meal (SBM) based on Z n depletion-repletion growth bioassays in young chicks. After a 4-d Zn depl etion period, chick weight gain responded linearly (P < .01) to graded incr ements of supplemental Zn (0 to 10 mg/kg) from ZnSO4. 7H(2)O, whether added to the Zn-deficient SPC or egg white diet. Slope, however, was over twice as great for the standard curve relating weight gain to supplemental Zn int ake for the egg white diet as for the SPC diet. Addition of 7 to 10 mg Zn/k g from SBM to either Zn-deficient diet increased (P < .01) weight gain, but a similar SBM addition to either diet made adequate in Zn did not increase weight gain. Using standard-curve methodology, REV of Zn in SBM was 78% wh en the the SPC diet was used, but it was only 40% when the egg white diet w as used. The phytate contained in the SPC basal diet therefore markedly red uced the efficiency of utilizing the supplemental inorganic Zn from ZnSO4. 7H(2)O. This lowered the slope of the standard curve so that, on a relative basis, the Zn in SBM had a higher REV value than was the case for Zn utili zation in SBM with the phytate-free egg white diet. The 78% Zn REV value in SBM would seem to have the greatest relevance for practical-type corn-SBM diets.