Effects of activated zinc oxide on growth performance, antioxidant capacity, and intestinal epithelial function in weaned pigs

Zinc oxide (ZnO) is commonly used to improve growth performance in weaned pigs, but its high-dose supplementation is increasingly restricted due to environmental concerns. Therefore, identifying effective alternatives at lower inclusion levels is of critical importance. This study evaluated activated zinc oxide (AZn) as a low-dose alternative by assessing its effects on growth performance, diarrhea incidence, nutrient digestibility, intestinal barrier function, and fecal zinc excretion in weaned pigs. A completely randomized design was used, in which 216 castrated male piglets (initial body weight 6.34 ± 0.16 kg; weaned at 21 days of age) were randomly assigned to six treatment groups, with six replicates per group and six piglets per replicate. The control group received a corn-soybean basal diet (NRC 2012) containing 100 mg/kg total Zn from feed ingredients and zinc sulfate (ZnSO₄). In the treatment groups, graded levels of AZn (125, 250, 500, or 1500 mg/kg Zn) or a single level of conventional ZnO (1500 mg/kg Zn) were added to the basal diet in place of the zinc sulfate in the premix. The trial lasted 28 d; on d 15, one pig per replicate closest to the pen mean was slaughtered. The results showed that compared with the control group, supplementation with AZn at any level or with 1,500 mg/kg ZnO improved growth performance and partial nutrient digestibility, and reduced diarrhea incidence (P < 0.05). At the 1,500 mg/kg supplementation level, fecal zinc concentration was lower in the AZn group than in the ZnO group (P < 0.05). Serum diamine oxidase activity was reduced in the AZn groups (125–500 mg/kg) compared with the control group (P < 0.05), whereas no such effect was observed in the ZnO group. Compared with the control group, both AZn and ZnO improved intestinal morphology and digestive enzyme activity (P < 0.05). Both also increased serum IgA and IgG concentrations and reduced malondialdehyde levels (P < 0.05), with no adverse effects on organ weights or hematological parameters (P > 0.05). In this study, AZn at 125–500 mg/kg showed comparable growth and diarrhea control to 1500 mg/kg ZnO, with no differences among the three lower doses. Regression analyses indicated optimal levels for intestinal function at approximately 440–560 mg/kg Zn, while fecal Zn at 250 mg/kg remained far below that at 1500 mg/kg. Considering both efficacy and environmental impact, a dietary AZn level of 250–500 mg/kg Zn is recommended.