Administration of vitamin D3 by injection or drinking water alters serum 25-hydroxycholecalciferol concentrations of nursery pigs

Objective: Two experiments were conducted to evaluate vitamin $D_3$ administration to nursery pigs by injection or in drinking water on serum 25-hydroxycholecalciferol ($25-OHD_3$) concentrations. Methods: At weaning, 51 pigs (27 and 24 pigs in experiments 1 and 2, respectively) were allotted to vitamin $D_3$ treatments. Treatments in experiment 1 were: i) control (CON), no vitamin administration beyond that in the diet, ii) intramuscular (IM) injection of 40,000 IU of vitamin $D_3$ at weaning, and iii) water administration, 5,493 IU of vitamin $D_3/L$ drinking water for 14 d post-weaning. Treatments in experiment 2 were: i) control (CON), no vitamin administration, and ii) water administration, 92 IU of $d-{\alpha}-tocopherol$ and 5,493 IU of vitamin $D_3/L$ drinking water for 28 d post-weaning. The lightest 2 pigs within each pen were IM injected with an additional 1,000 IU of $d-{\alpha}-tocopherol$, 100,000 IU of retinyl palmitate, and 100,000 IU of vitamin $D_3$. Results: In both experiments, serum $25-OHD_3$ was changed after vitamin $D_3$ administration (p<0.05). In experiment 1, injection and water groups had greater values than CON group through d 35 and 21 post-administration, respectively (p<0.05). In experiment 2, serum values peaked at d 3 post-administration in the injection groups regardless of water treatments (p<0.05) whereas CON and water-only groups had peaks at d 14 and 28 post-administration, respectively (p<0.05). Even though the injection groups had greater serum $25-OHD_3$ concentrations than the non-injection groups through d 7 post-administration regardless of water treatments (p<0.05), the water-only group had greater values than the injection-only group from d 21 post-administration onward (p<0.05). Conclusion: Serum $25-OHD_3$ concentrations in pigs increased either by vitamin $D_3$ injection or drinking water administration. Although a single vitamin $D_3$ injection enhanced serum $25-OHD_3$ concentrations greater than water administration in the initial period post-administration, a continuous supply of vitamin $D_3$ via drinking water could maintain higher serum values than the single injection.