Impact of dietary vitamin D3 supplements in nursery diets on subsequent growth and bone responses of pigs during an immune challenge.

Limited evidence is available to validate beneficial responses from extra nutrient supplements for mediation of growth suppression that results from immune challenges. Extrarenal roles of vitamin D metabolites in immune function implicate vitamin D3 supplements as a nutrient for potential beneficial effects. The current objective was to assess growth and bone ash responses to dietary vitamin D3 (D) supplements for growing pigs undergoing an immune challenge. At weaning, 216 crossbred pigs (4 pigs/pen, 6 pens/treatment) were randomly allotted within sex and weight blocks to 1 of the 9 treatments. Treatments included D supplements (0, 100, or 800 IU/kg) in a factorial arrangement with 3 vaccine (V) protocols; no injection (0 × V), a single 2 mL injection of a Lawsonia intracellularis vaccine at day 14 (1 × V), or 2 mL injections of the same vaccine at days 0 and 7 (2 × V). An adjustment diet with no supplemental D was fed for 1 wk, then assigned D diets for 2 wk (P2). After P2, all pigs were phase-fed standard diets (D = 280 IU/kg) to assess subsequent growth to 115 kg. No differences due to D supplements or vaccination protocol were detected in ADG (0.233 ± 0.021 kg/d) or GF (0.642 ± 0.028 kg/d) over the 21-d nursery trial; however, ADFI was lower (P < 0.10) in pigs fed D levels of 0 vs. 100 and 800 (0.340 vs. 0.375, 0.372 ± 0.027 kg/d). Bone mineral content (g) from whole-body dual energy X-ray absorptiometry scans at 9 wk (n = 4 pigs/treatment) was lower in pigs fed 0 vs. 100 and 800 IU of D (287 vs. 325, 323 ± 34.1 g/pig). Growth from nursery to 115 kg was lower (P < 0.01) in pigs fed D levels of 0 vs.100 and 800 (0.828 vs. 0.876, 0.889 ± 0.021 kg/d). At market, approximately two-thirds of pigs showed positive L. intracellularis serology titers regardless of treatment. Limited evidence for D-mediation of an immune challenge using the vaccination protocols may be a consequence of limited vaccine effects on growth in the nursery and seroconversion of most pigs to L. intracellularis by market.