GROWTH AND PLASMA ZINC RESPONSES OF YOUNG-PIGS FED PHARMACOLOGICAL 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 < .01) for all three sources of Zn, although slopes of the ZnO and Zn-Lys response curves were 56% (P < .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 < .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 < .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 < .05) than those in pigs fed ZnO.