Intramammary 25-hydroxyvitamin D3 and 1,25-dihydroxyvitamin D3 treatments differentially increase serum calcium and milk cell gene expression

[Display omitted] •Intramammary 1,25-dihydroxyvitamin D increased serum Ca concentrations compared with serum 25-hydroxyvitamin D and placebo.•Intramammary 25-hydroxyvitamin D did not increase serum Ca concentration compared with placebo.•Intramammary 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D treatments increased milk somatic cell CYP24A1 and NOS2A expression. Intramammary 25-hydroxyvitamin D3 (25D) and 1,25-dihydroxyvitamin D3 (1,25D) treatments stimulate immune defenses of the mammary gland. We hypothesized 25D treatment, in contrast to 1,25D, would exert activity in the mammary gland without affecting serum calcium. The objective was to determine the effect of dose and source of intramammary vitamin D treatments on milk somatic cell gene expression and serum calcium. Twenty lactating Holstein cows with somatic cell count