Plasma transport of ergocalciferol and cholecalciferol and their 25-hydroxylated metabolites in dairy cows.

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Hymoller L, Jensen SK

Plasma transport of ergocalciferol and cholecalciferol and their 25-hydroxylated metabolites in dairy cows.

Domest Anim Endocrinol. 2017 Apr;59:44-52. doi: 10.1016/j.domaniend.2016.11.002. Epub 2016 Nov 16.

PubMed ID
27940098 [ View in PubMed
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Abstract

In cattle, there are 2 significant forms of vitamin D: ergocalciferol (ERG) from fungi on roughage and cholecalciferol (CHO) from vitamin supplements or endogenous synthesis in the skin. The hypothesis of the present study is that vitamin D from the 3 sources is transported in different plasma fractions in the body. This is hypothesized to explain the lower efficiency of ERG compared to CHO in securing a sufficient plasma status of 25-hydroxyvitamin D and explain the inefficient excretion of dietary CHO into milk compared to endogenous CHO. Twenty vitamin D-depleted cows were assigned to 5 treatments: D2, housed indoor and fed 625-mug/d (25.000 IU) ERG; D3, housed indoor and fed 625-mug/d CHO; D2+D3, housed indoor and fed 625-mug/d ERG and 625-mug/d CHO; SUN, let out for daily pasture to facilitate CHO synthesis from sunlight; and D2+SUN, fed 625-mug/d ERG and let out for daily pasture. Blood samples were taken twice weekly and plasma fractionated by ultracentrifugation into 3 fractions: light lipoprotein (LLP), heavy lipoprotein (HLP), and protein and analyzed for content of ERG and CHO and their liver derived metabolites 25-hydroxyergocalciferol (25ERG) and 25-hydroxycholecalciferol (25CHO), respectively. Liver biopsies were taken on the last day of the study to asses gene expression related to vitamin D metabolism. During 4 wk of study, the vitamin D status in plasma increased to 19.3 to 22.8 ng/mL 25ERG in ERG-treated cows with the highest concentration in D2 (P

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