Background: Zinc (Zn) supplementation has been shown to reduce the incidence of diarrhea and to protect animals from intestinal diseases, but the mechanisms of this protective effect against virus infection in vivo have not yet been elucidated. Transmissible gastroenteritis virus (TGEV) causes diarrhea in piglets with an age-dependent decrease of severity.
Results: We used 60 weaned piglets that were divided into three groups to evaluate the effect of different Zn levels added to a conventional diet (50 mg Zn/kg diet, Znlow, control group). The other groups received the diet supplemented with ZnO at final concentrations of 150 mg Zn/kg diet (Znmed), or 2,500 mg/kg diet (Znhigh). Oral challenge infection with TGEV was performed when the pigs had been fed for 1 week with the respective diet. Half of the piglets of each group were sacrificed at day 1 and 18 after challenge infection. Fecal consistency was improved and body weights increased in the Znhigh group when compared to the other groups, but no direct effect of Zn concentrations in the diet on fecal TGEV shedding and mucosal immune responses was detectable. However, in the Znhigh group, we found a prevention of villus atrophy and decreased caspase-3-mediated apoptosis of jejunal epithelium. Furthermore, pigs receiving high Zn diet showed a down-regulation of interferon (IFN)-α, oligoadenylate synthetase (OAS), Zn transporter SLC39A4 (ZIP4), but up-regulation of metallothionein-1 (MT1), as well as the Zn transporters SLC30A1 (ZnT1) and SLC30A5 (ZnT5). In addition, forskolin-induced chloride secretion and epithelial resistance were controlled at a physiological level in the Znhigh but not the other groups. Finally, in the Znhigh group, we documented an earlier and higher systemic TGEV-specific serum antibody response.
Conclusions: These results suggest that high dietary Zn could provide enhanced protection in the intestinal tract and stimulate the systemic humoral immune response against TGEV infection.