Relative bioavailabilities of organic zinc sources with different chelation strengths for broilers fed a conventional corn-soybean meal diet

An experiment was conducted to estimate relative bioavailability of Zn in 3 organic zinc sources with different chelation strength (Qf) compared with ZnSO₄. A total of 1,092, 1-d-old male broiler chicks were assigned randomly to 6 replicate cages (14 chicks per cage) for each of 13 treatments. Dietary treatments included the basal corn-soybean meal diet (27.82 mg of Zn/kg of DM) supplemented with 0, 30, 60, or 90 mg of added Zn as reagent ZnSO₄, or Zn sources with Qf of 6.5 (11.93% Zn; Zn AA C), 30.7 (13.27% Zn; Zn Pro B), or 944.0 (18.61% Zn; Zn Pro A)/kg, which are considered as weak, moderate, or strong Qf, respectively. Bone Zn, pancreas Zn, pancreas metallothionein (MT) concentration, and pancreas MT messenger RNA (mRNA) were analyzed at 6, 10, or 14 d of age. The results showed that bone Zn, pancreas Zn, pancreas MT concentration, and pancreas MT mRNA increased linearly (P < 0.001) as dietary Zn concentration increased at all ages. At 6 d of age, pancreas MT mRNA differed (P < 0.001) among dietary Zn sources, and the same tendency was observed at 10 (P = 0.08) or 14 d (P = 0.06) of age. The R² for a linear model was greater on d 6 than d 10 or 14 for all the response criteria. Based on slope ratios from the multiple linear regression of pancreas MT mRNA concentration on daily intake of dietary Zn, the bioavailability of Zn AA C, Zn Pro B, and Zn Pro A relative to ZnSO₄ (100%) were 100.0, 121.1, and 72.3%, respectively, at 6 d of age. The results indicated that MT mRNA concentration in pancreas was more sensitive in reflecting differences in bioavailability among organic Zn sources than the MT concentration in pancreas or other indices. Moreover, the bioavailability of organic Zn sources was closely related to their Qf.