262 Modulation of vitamin D, calcium and phosphorous metabolism and immune response in pre- and post-weaning piglets under different vitamin D supplementation strategies

Abstract This study evaluated the impact of different vitamin D supplementation strategies to pre- and post-weaning piglets on vitamin D, calcium and phosphorous metabolism and immune status. Sixty piglets were selected at d 2 of age [body weight (BW) = 1.71 ± 0.03 kg] and orally supplemented with saline (CTR) or a solution of 25(OH)D3 at d 2, d 8, and d 21 (0.1, 0.2 and 0.3 mg, respectively) along with UVB exposure every second day from d1 4 up to d 21 (HD). From weaning (d 21) until d 42, CTR animals were supplemented with 2,000 UI of vitamin D3/kg of feed and HD animals were supplemented with 2,000 UI 25(OH)D3/kg. Piglets were sacrificed at d 21, d 28, and d 35 (n = 10/treatment/d) for the collection of blood, jejunum, liver, and kidney samples. Serum 25(OH)D3 concentrations were determined by HPLC and the mRNA expression of genes implicated in vitamin D, calcium and phosphorous metabolism and immune status were assessed by quantitative real-time PCR. Data were analyzed using a 2x3 factorial design. Serum 25(OH)D3 concentrations were 2.8, 3.6, and 2.2-fold greater in HD piglets at d 21, 28, and 35 (P ≤ 0.01), respectively (Table 1). No treatment or treatment x time interaction was detected on the expression of genes related to vitamin D metabolism in the jejunum mucosa and liver (P ≥ 0.19). In kidney, HD piglets had greater expression of CYP27B1 (P = 0.09) and decreased expression of CYP24A1 (P = 0.06). Renal EGR1 expression was greater in HD piglets (P = 0.01). No treatment effect was detected on the expression of genes directly implicated in phosphate or calcium reabsorption (P ≥ 0.16). No treatment or treatment x time interaction was detected on the mRNA expression of selected genes related to immune response in the jejunum mucosa, liver, and kidney (P ≥ 0.14). Independently of vitamin D treatments, time effects were detected for gene expression. The mRNA expression of CYP27B1 increased and that of CYP24A1 decreased from d 28 to 35 (P ≤ 0.04) in kidney. Genes related to calcium (TRPV5) and phosphate (NPT2c) reabsorption in kidney had reduced mRNA expression on d 35 compared with d 21 (P ≤ 0.01). Overall, the mRNA expression of genes related to immune response in all studied tissues was lower at d 35 compared with d 21 (P ≤ 0.08). Bodyweight at slaughter was not affected by treatments at d 21, 28, and 35 (P ≥ 0.29). In conclusion, pre-weaning vitamin D supplementation enhanced vitamin D status at weaning and the use of dietary 25(OH)D3 supplementation was more effective in increasing the vitamin D status post-weaning. The mRNA expression results suggest that greater vitamin D status at weaning and during the first 2 wk post-weaning do not affect calcium and phosphate reabsorption in kidney and the immune defense of pre- and post-weaning piglets.