Effect of supplementation of vitamin D or vitamin D on serum concentrations of free and total 25-hydroxyvitamin D and the expression of genes involved in immune function in peripheral blood mononuclear cells of weaned pigs.

The present study aimed to compare the effects of vitamin D and vitamin D supplementation on concentrations of total and free 25(OH)D in plasma and the expression of genes involved in the innate immune system in peripheral blood mononuclear cells (PBMC) in weaned pigs. Five groups of pigs (with an initial body weight of around 9 kg) received basal diets supplemented with either 500 (control group), 1000 or 2000 IU vitamin D/kg diet or 1000 or 2000 IU vitamin D/kg diet for a period of 4 weeks. Vitamin D supplementation did not influence feed intake, body weight gain, feed conversion ratio, apparent total tract digestibility of calcium and phosphorus, and serum concentrations of calcium, inorganic phosphate and parathyroid hormone. Supplementation of vitamin D led to a dose-dependent increase of the concentrations of total and free 25(OH)D in serum. In contrast, pigs supplemented with 1000 or 2000 IU vitamin D/kg diet did not have higher concentrations of total and free 25(OH)D in serum than the control group. The ratio of free/total 25(OH)D in serum was not influenced by vitamin D supplementation, whereas the group supplemented with 2000 IU vitamin D/kg diet had a higher free/total 25(OH)D ratio than the groups supplemented with 1000 or 2000 IU vitamin D/kg diet. Genes involved in vitamin D signalling (), as well as pro-inflammatory and immune regulatory genes ( and ) and genes encoding porcine protegrins (), proteins belonging to the group of antimicrobial peptides, in PBMC were not different among groups supplemented with vitamin D or vitamin D and the control group. Therefore, the study indicates that supplementation of vitamin D causes much lower levels of total 25(OH)D than supplementation of vitamin D and that supplementation of vitamins D or D at moderate levels does not have an impact on the innate immune function in healthy pigs.