Effect of dietary zinc oxide on jejunal morphological and immunological characteristics in weaned piglets

The aim of this study was to evaluate age-related changes and the effect of dietary Zn concentration on morphological and immunological characteristics in the gastrointestinal tract of piglets. A total of 96 purebred Landrace piglets were weaned at the age of 26 ± 1 d, and randomly allocated into 3 treatment groups fed with low (57 mg Zn/kg), medium (164 mg Zn/kg), and high (2425 mg Zn/kg) dietary Zn (ZnO). Piglets (4 males and 4 females per treatment group) were killed at 33 ± 1, 40 ± 1, 47 ± 1, and 54 ± 1 d of age. In the jejunum, villus height, crypt depth, and the number of goblet cells producing neutral, acidic, sulfated, and sialylated mucins were measured. Intraepithelial lymphocytes were characterized by flow cytometry and the gene expression of mucin 2 (MUC2), mucin 20 (MUC20), β-defensin 3, and trefoil factor 3 (TFF3) was determined by reverse transcription quantitative PCR. Villus height and crypt depth in the jejunum showed age related differences (P < 0.01), whereas the dietary concentrations of Zn had no effect. The mucin types were modified mainly by age, and dietary Zn had no effect in the proximal jejunum. In the distal jejunum, age and Zn had effects on the mucin types. The abundance of sulfomucins decreased (P < 0.001) and sialomucins increased with age (P < 0.001), while high dietary ZnO reduced the sulfomucins (P < 0.001) and increased the sialomucins (P < 0.05) in the crypts. The phenotypes of lymphocytes in the epithelium of the proximal jejunum showed relatively constant percentages of T-cells, as well as natural killer cells. High dietary Zn treatment led to a reduced abundance of CD8(+) γδ T-cells (P < 0.05). The apportionment of different cytotoxic T-cell was age dependent. Although the percentage of CD4(-)CD8β(+) increased (P < 0.01), the relative amount of CD4(+)CD8β(+) decreased with age (P < 0.05). The expression of MUC2 and MUC20 was not influenced by age or dietary Zn concentration. High Zn intakes resulted in a reduced gene expression of β-defensin 3 (P < 0.05), but did not affect the expression of TFF3. It is concluded that Zn in the form of ZnO appears to have specific effects on the innate and adaptive gut associated immune system of piglets. These might contribute to the positive effects of Zn on the prevention of postweaning diarrhea.