Variation in ovine serum vitamin D concentrations from late summer to early spring and during immune challenge with bacterial endotoxin.

Vitamin D is most known for its role in the development and maintenance of the skeletal system. However, recent studies have found that vitamin D modulates the immune system, and at sufficient levels supports optimal immune function. Previous research has examined how vitamin D levels change seasonally and during immune stress challenges in both humans and cattle, but not sheep. Our study aimed to investigate the changes in the vitamin D status of sheep throughout the year in Southern Ontario as well as in response to a bacterial endotoxin challenge. Vitamin D was found to be significantly lower in spring when compared to summer and early winter levels. No significant differences were found in vitamin D levels among any measured time points during the immune challenge, although a trending increase was found 4 hr post-challenge. Overall, this study demonstrated how vitamin D levels in sheep change throughout the year, and slightly during endotoxin challenge. Given the importance of vitamin D in regulating optimal immune function, more investigation of these changes in vitamin D levels is warranted in terms of supporting optimal immune function.