Deposition and transport of trace mineral elements were affected by stocking density in fattening pigs

Trace minerals are important for balanced nutrition in pigs and to maintain pig growth under high stocking densities. To study the effects of stocking density on serum and liver trace mineral deposition in fattening pigs, 288 conventional pigs (Duroc × Landrace × Large) were selected and assigned to one of three groups: low, medium or high density (8, 16, or 24 pigs, respectively, per 5.2 m × 3.8 m pen). On d 30, one pig per pen was chosen, blood samples were taken, and the pigs were sacrificed; liver and intestinal mucosa samples were obtained from these pigs for trace mineral determination and RT-PCR. The results showed that compared with those of the low-density group, serum Fe, Zn, and Mn concentrations significantly decreased (P < 0.05), while liver Fe and Mn significantly increased in both the medium- and high-density groups (P < 0.05). mRNA expression of ATP7A, ATP7B, FRRS1, and SLC30A3 transporters was significantly upregulated in the liver of the medium-density group, and FRRS1 and SLC1A2 expression in the liver, MT-2b in the jejunal mucosa, and SLC11A2 (DMT1) and FRRS1 in the ileal mucosa were upregulated in the high-density group (P < 0.05). Alternatively, ATX1 expression in the jejunal mucosa of the medium-density group, SLC30A9 in the duodenal and jejunal mucosa, ATX1 in the jejunal mucosa, and MT-2b in the ileal mucosa of the high-density group were downregulated (P < 0.05). These results demonstrated that stocking density affected serum Fe, Zn, and Mn, as well as liver Fe and Mn. Stocking density also affected mRNA expression of trace mineral transporters in both the liver and intestinal mucosa of fattening pigs under the studied conditions.