Greater Bioavailability of Chelated Compared with Inorganic Zinc in Broiler Chicks in the Presence or Absence of Elevated Calcium and Phosphorus

Animal diets often contain antagonists that reduce Zn bioavailability, thereby creating a deficiency. The bioavailability of Zn chelated to 2-hydroxy-4-(methylthio)butanoic acid (chelated Zn) was compared with Zn sulfate in broiler chicks in two dietary conditions: a Zn-deficient corn-soybean meal (C-SBM) diet and a Zn-deficient C-SBM diet containing elevated Ca and P as antagonists. In experiment 1, chicks were fed a common diet (19 mg Zn/kg diet) through day 8, and then a Zn-unsupplemented (21 mg Zn/kg diet; 0.82% Ca, 0.47% available P) C-SBM basal or the basal supplemented with 5, 10, 15, 20, or 30 mg Zn/kg diet as chelated Zn or Zn sulfate for 6 days. Common-intercept, multiple linear regression slope-ratio analysis indicated significantly greater Zn bioavailability for chelated Zn relative to Zn sulfate as judged by: total tibia Zn (µg) (161%; =0.001); tibia zinc concentration (µg/g; 165%, =0.0009); and small intestinal metallothionein mRNA expression (248%; =0.009). In experiment 2, chicks were fed a Zn-deficient (24 mg Zn/kg diet) common diet, then fed a C-SBM basal elevated in Ca and P (27 mg Zn/kg diet; 1.2% Ca, 1% available P), or the basal supplemented with 15 or 30 mg Zn/kg diet as Zn sulfate or 7.5, 15, or 30 mg Zn/kg diet as chelated Zn. Zn sulfate was antagonized to a greater extent than Zn chelate. Bioavailability of chelated Zn relative to Zn sulfate was 441% ( =0.0063; µg total tibia Zn), 307% ( =0.0066; µg/g tibia Zn), and 426% ( =0.0041; metallothionein). Thus, feeding chelated Zn offers advantages over inorganic Zn, especially in diets containing high levels of Ca and P, which is a common occurrence in pet food and in livestock diets. antagonism, broilers, chelate, metallothionein, minerals