Effects of nano zinc oxide as an alternative to pharmacological dose of zinc oxide on growth performance, diarrhea, immune responses, and intestinal microflora profile in weaned piglets

The effects of nano zinc oxide (nano-ZnO) on growth performance, diarrhea incidence, immune responses, antioxidant capacity, intestinal microflora, and volatile fatty acid concentrations in weaned piglets were investigated. Crossbred weaned piglets (n = 216), weighing 8.88 +/- 1.14 kg, were randomly assigned to one of six treatments with six replicates of six piglets (3 females and 3 castrated males) per treatment fed corn-soybean meal-based diets supplemented with 2.0 g/kg Zn as ZnO, or 0 (control), 0.3, 0.4, 0.5 or 0.6 g/kg Zn as nano-ZnO for 14 days. Selected piglets (n = 36, one piglet per pen) were euthanized on day 14, and the remaining piglets were all fed the same diet from days 15 to 28. During days 1-14 or 1-28, nano-ZnO inclusion in diets improved average daily gain (linear P < 0.05) and reduced diarrhea incidence in weaned piglets (linear P < 0.01; quadratic P < 0.05). On day 14, increased nano-ZnO supplementation elevated the serum concentrations of alkaline phosphatase, immunoglobulin G (IgG) and superoxide dismutase linearly and quadratically (P < 0.01 and P < 0.05), and linearly increased serum levels of insulin and immunoglobulin M (IgM) and the concentrations of superoxide dismutase and metallothionein in the liver (P < 0.01 and P < 0.05). In addition, malondialdehyde concentrations in serum and liver decreased linearly or quadratically as nano-ZnO levels increased (P < 0.01 and P < 0.05). Nano-ZnO inclusion increased the number of lactic acid bacteria and total anaerobic bacteria, and elevated concentrations of acetic acid and total volatile fatty acids in the ileal and cecal digesta linearly or quadratically (P < 0.01 and P < 0.05), while nano-ZnO linearly decreased the numbers of E. coli in the cecal digesta (P < 0.01). There was no difference between pigs fed with 0.6 g/kg nano-ZnO and pigs fed with 2000 g/kg ZnO in these parameters from days 1 to 14. Among all the treatments, no difference was observed in growth performance during days 15-28, and the serum concentrations of insulin, IgG, IgM, immunoglobulin A (IgA), superoxide dismutase, and malondialdehyde were also not different on day 28 (P > 0.05). The overall results indicate that dietary supplementation with 0.6 g/kg Zn as nano-ZnO is comparable to pharmacological doses of ZnO (2.0 g/kg Zn) in terms of improving growth performance, reducing diarrhea incidence, enhancing serum immune levels, and promoting antioxidant capacity, as well as regulating the intestinal microflora profile in piglets during days 1-14 after weaning.