Supplementing weanling pigs with high concentrations of Zn and the Zn availability of Zn sources for weanling pigs
Thirteen trials (n=930) were conducted to investigate the supplementation of weanling pigs with high levels of Zn and to compare the availability of Zn from several Zn sources for weanling pigs. In the first four trials, supplementing Zn by injecting Zn acetate either i.m. or i.p. at various times near weaning did not improve postweaning growth performance compared with pigs that were not injected. Additionally, stressing pigs by regrouping and then injecting Zn acetate did not improve growth performance. Serum Zn concentrations were increased in all of the trials by the injection of Zn. In the next five trials, feeding 3,000, 2,000 or 1,000 mg Zn/kg of diet from ZnSO₄, Zn-lysine or Zn-methionine did not improve growth performance immediately after weaning compared with pigs fed diets with 105 mg Zn/kg of diet. Feeding 3,000 mg Zn/kg of diet as ZnO (P < .05) improved growth performance above that of pigs fed 3,000 mg Zn/kg of diet from the other sources, but did not improve growth performance compared to controls. Lower tissue Zn concentrations suggested a lower availability of Zn from ZnO compared with ZnSO₄, Zn-lysine and Zn-methionine. There was little difference in Zn availability among the other sources. In the next three trials, feeding diets with different levels of lysine had little influence on the availability of Zn from Zn-lysine compared to ZnSO₄. Results indicate that Zn from Zn-lysine is not absorbed in conjunction with the lysine component of the complex. Additionally, there were no differences in the availability of Zn from ZnSO₄ compared to Zn-lysine. In the last trial, Zn from ZnO was less available (P < .05) to Zn deficient pigs than ZnSO₄, Zn-lysine or Zn-methionine when rib bone Zn concentration was used as an indicator of Zn availability. In summary, supplementing weanling pigs with high levels of Zn immediately before or after weaning does not appear to improve growth performance. Furthermore, Zn from ZnO is less available to weanling pigs than Zn from ZnSO₄, Zn-lysine or Zn-methionine.