Dairy cows undergo dramatic metabolic changes and impaired immune system function in the transition period; thus, they are very susceptible to peripartum disease. Vitamin D as an immune-modulatory agent may have protective effects against oxidative stress and numerous diseases. Our objective in this study was to investigate the changes in 25(OH)D concentrations in dairy cattle during the transition period and its association with some inflammatory and oxidative stress markers. Twenty-three healthy cows were selected from two commercial farms and were sampled 1 week prepartum and 1 week and 3 weeks postpartum. 25(OH)D, IL-4, IL-10, INF-γ, Hap, IgG, MDA, and TAC amounts were measured. Time had significant effects on 25(OH)D concentrations and its concentration was decreased 1 week after parturition and then increased. The consumption of vitamin D for calcium homeostasis and the proper immune system functioning may be the reason for decreasing in its amounts after parturition. Pearson test showed that in 1 week prepartum, 25(OH)D levels tended to be significantly correlated with IL-4 (P = 0.076) and IgG (P = 0.058) levels. No significant correlation was observed between 25(OH)D levels and other measured variables in the first and third weeks after parturition. It should be noted that the amount of 25(OH)D in the first week after calving reaches to its lowest level, which may leads to impaired immune system function and increased susceptibility of dairy cows to disease.

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