The Effects of Partially or Completely Substituted Dietary Zinc Sulfate by Lower Levels of Zinc Methionine on Growth Performance, Apparent Total Tract Digestibility, Immune Function, and Visceral Indices in Weaned Piglets

SIMPLE SUMMARY: This study was conducted to assess the effects of five diets with different doses and sources of zinc (Zn) on the growth performance (average daily gain, average daily food intake and gain to feed ratio), apparent total tract digestibility of nutrients, serum metabolites and immune functions of weaned piglets. The control diet contained 100 mg/kg inorganic Zn from ZnSO(4). The total dose of Zn in experimental diets was lower than that of the control diet, and the inorganic Zn from ZnSO(4) was gradually replaced by organic Zn from ZnMet. Therefore, the experimental diets were a basal diet containing 75 + 12.5, 50 + 25, 25 + 37.5, and 0 + 50 mg/kg Zn from ZnSO(4) and ZnMet, respectively. No differences were observed in growth performance, nutrient digestibility and serum metabolites. However, Zinc digestibility and parameters relating to body immune functions were improved when at least 50 mg of inorganic Zn was replaced by organic Zn. Thus supplementing 50 mg of inorganic Zn from ZnSO(4) plus 25 mg of organic Zn from ZnMet to piglets would be the best strategy to benefit the immune system and maintain growth performance under the conditions of the current study. ABSTRACT: The study aimed to evaluate the effects of replacing zinc sulfate (ZnSO(4)) with a lower level of zinc methionine (ZnMet) on the growth performance, apparent total tract digestibility (ATTD) of nutrients, serum metabolites and immune functions of weaned piglets. Thirty-five weaned Duroc × Landrace × Large White male piglets (10.69 ± 0.26 kg) were randomly allotted to five diets. The control diet was supplemented with 100 mg/kg of Zn from ZnSO(4), and experimental diets included 75 + 12.5, 50 + 25, 25 + 37.5, and 0 + 50 mg/kg of Zn from ZnSO(4) and ZnMet, respectively. The results showed that no differences were observed in growth performance, ATTD of nutrients and serum metabolites among treatments, while serum white blood cell count, lymphocyte count, IgM contents and spleen index were higher (p < 0.01) in piglets fed with 50 + 25 mg/kg of Zn. Zinc digestibility (p < 0.05), IgA content (p < 0.001) and thymus index (p < 0.05) were increased when at least 50% of ZnSO(4) was replaced by ZnMet. All the results indicated that using a lower level of ZnMet in weaned piglet’s diet instead of ZnSO(4) had no adverse impacts on ATTD of nutrients and serum metabolites; and a 50 + 25 mg/kg of Zn (from ZnSO(4) and ZnMet, respectively) diet showed the best advantages for parameters relating to immune functions.