Zinc stores in chickens delay the onset of zinc deficiency symptoms

Three chick assays were conducted to evaluate Zn depletion rates in whole body and various tissues. In Assay 1, chicks fed a corn-soybean meal diet containing 1,037 mg Zn/kg had twice as much Zn in intestine and bone and 50% more Zn in liver and whole body than chicks fed 37 mg Zn/kg (P < .01). In Assay 2, the minimum Zn requirement for growth of chicks consuming a chemically defined, amino acid diet was 10.6 mg Zn/kg. In Assay 3, chicks were fed the chemically defined diet containing either 300 or 10.6 mg Zn/kg during an 8-d pretest period, after which they were fed either 0 or 10.6 mg Zn/kg for 9 d. Tissue Zn concentrations were determined on Days 0, 1, 2, 3, 4, 5, 7, and 9 of the test period. Following the pretest period, Zn was higher in the liver, tibia, and small intestine, but not in muscle, of chicks fed 300 mg Zn/kg than of those fed 10.6 mg Zn/kg (P < .01). Growth of chicks switched from 10.6 to 0 mg Zn/kg was less than for chicks maintained on 10.6 mg Zn/kg by Day 5 (P < .05), whereas chicks switched from 300 to 0 mg Zn/kg did not display a growth depression relative to the control until Day 8 (P < .05). Zinc that accumulated in the liver and small intestine of chicks fed the 300 to 0 Zn regimen declined until Day 3 of the test period, whereas tibia Zn decreased until Day 8. Chicks fed the 10.6 to 0 regimen did not display a substantial decrease in small intestine, liver, or tibia Zn. The data confirm that Zn can accumulate in bone, liver, and intestine and can subsequently be released for use during a period of Zn deficiency. The data also indicate that chicks fed a diet containing the minimum requirement of Zn cannot accumulate reserves of Zn that become available for use during a subsequent period of Zn depletion.