Growth and plasma zinc responses of young pigs fed pharmacologic levels of zinc

Three trials were conducted to evaluate high levels of Zn addition from various Zn sources on growth performance and plasma Zn responses of 8-kg pigs. Zinc supplements were added to 20% CP starting diets (125 mg of Zn/kg) containing antibiotics. Trial 1 was done to evaluate plasma Zn responses of pigs fed three different feed-grade Zn sources: ZnO where supplemental Zn levels were 0, 250, 500, 1,000, 3,000, and 5,000 mg/kg; ZnSO4 at 1,500 or 2,500 mg of Zn/kg; and a zinc-lysine complex (Zn-Lys) at 1,500 or 2,500 mg of Zn/kg. Plasma Zn concentration as a function of supplemental Zn intake was fitted to a broken-line for ZnO data and to simple linear models for ZnSO4 and Zn-Lys data. For ZnO, plasma Zn did not increase until concentrations 1,000 mg Zn/kg were fed. Above this level, plasma Zn increased linearly (P 0.01) for all three sources of Zn, although slopes of the ZnO and Zn-Lys response curves were 56% (P 0.05) and 110%, respectively, of the ZnSO4 slopes. In Trial 2, five diets were fed: basal, 3,000 and 5,000 mg of Zn/kg from ZnO, and 3,000 and 5,000 mg of Zn/kg from ZnSO4. Daily gain and daily feed intake were increased (P 0.05) by ZnO addition, regardless of level, whereas ZnSO4 addition increased these performance indices only at the 3,000 mg of Zn/kg level of supplementation. Plasma Zn responses to ZnSO4 addition were almost double those of ZnO addition. Trial 3 involved a basal starting diet fortified with both plasma protein and fish meal, and 3,000 mg of Zn/kg from ZnO elicited gain and feed intake responses (P 0.05), whereas 3,000 mg of Zn/kg from ZnSO4 or Zn methionine (Zn-Met) or 250 mg of Cu/kg from CuSO4 did not elicit a response. Plasma Zn concentrations in pigs fed ZnSO4 or Zn-Met were substantially higher (P 0.05) than those in pigs fed ZnO