184 The metabolism of vitamin D is modulated by vitamin C supplementation during porcine reproductive and respiratory syndrome challenge in post-weaning piglets

Abstract

Abstract This study evaluated the impact of different dietary vitamin D sources combined or not with vitamin C on serum 25(OH)D3 concentrations and the expression of genes related to antimicrobial peptides and to the metabolism of vitamin D, vitamin C, calcium (Ca), and phosphorus (P). From weaning (d 21) until d 68, 27 piglets were fed a post-weaning diet supplemented with: 1,500 IU of vitamin D3 (CTR; n = 9); 200 IU of vitamin D3 + 2,000 IU of 25(OH)D3 (HD; n = 8); or HD + 500 mg/kg of vitamin C (HD+C; n = 10). From d 40 to 68 piglets were exposed to porcine reproductive and respiratory syndrome (PRRS) using a natural disease challenge model. At d 68, after blood collection, all piglets were euthanized for the collection of lung and kidney samples. The concentrations of serum 25(OH)D3 were determined by HPLC and the mRNA expression of genes of interest was assessed by qPCR. Data were analyzed in a one-way analysis of variance with three treatments. At d 40 (after 19 d of supplementation), serum 25(OH)D3 concentrations were greatest for HD+C (22.48 ± 1.25 ng/mL), intermediate for HD (17.43 ± 0.84 ng/mL), and least for CTR (8.54 ± 0.65 ng/mL) treatments (P < 0.01). At d 68 (after 28 d of PRRS challenge) these values were greatest for HD (14.64 ± 2.77 ng/mL), intermediate for CTR (6.22 ± 0.59 ng/mL), and least for HD+C (2.18 ± 0.13 ng/mL; P < 0.01). No treatments effect was detected on pulmonary CYP27B1, RXRα, SLC23A1, RIGI, PR-39, and pBD1. In lungs, VDR expression was least for HD+C (P ≤ 0.06) whereas MDA5 expression was greatest for HD+C (P ≤ 0.07), and SLC23A2 expression was greatest for HD (P ≤ 0.09; Table 1). No treatments effect was detected on expression of renal FGFR1, KL, RXRα, SLC23A1, SLC23A2, and TPRV5. In kidney, CYP27B1 expression was greatest for HD+C groups (P = 0.03) and CYP24A expression was greatest for HD (P = 0.01). Renal EGR1 and NPT2c expressions were greatest for CTR groups and least for HD+C (P = 0.09) whereas WNK4 expression was greatest for HD+C and least for CTR (P = 0.10). Renal VDR expression was greatest for HD groups and least for HD+C (P ≤ 0.05). In conclusion, vitamin C supplementation increased serum 25(OH)D3 concentrations in pre-challenged piglets. These concentrations were reduced by vitamin C supplementation after PRRS challenge, which may be related to a greater synthesis of the active form of vitamin D in the kidney. Little effects were detected on pulmonary antimicrobial peptides, but the gene expression related to renal P reabsorption was influenced by HD+C whereas Ca reabsorption was apparently not impacted by treatments.