Vitamin D belongs to the group of fat-soluble vitamins, and many consider it a hormone due to its functions.
Its main role is linked to calcium homeostasis, but it also acts on the immune system, cell differentiation, and cell proliferation.
First, this vitamin/hormone can be found in plants/fungi, under the name of ergocalciferol, and called vitamin D2. It is based on animals called cholecalciferol, known as vitamin D3. Animals can acquire vitamin D in several ways, consuming forages that have ergocalciferol, exposure to sunlight, feed, and injections.
However, cholecalciferol (D3) is the form used in animal supplementation. It is obtained through sun exposure when the precursor 7 – dehydrocholesterol is irradiated with UVB light and is converted into cholecalciferol. However, even animals producing their vitamin D, it is not difficult to see animals with vitamin D deficiency. And this can be more noticeable in regions where there are large variations in photoperiod, as in the polar and temperate regions. With prolonged exposure to UVB previtamin D3 is subject to photodegradation into inactive substances.
After intestinal absorption and synthesis in the skin, vitamins D2 and D3 are transported to the liver, where they are hydroxylated for the first time to form 25-hydroxyvitamin D (25-OHD) / calcidiol. The second hydroxylation (by 1α-hydroxylase) occurs in the kidney’s proximal tubules to form an active form of vitamin D called calcitriol / 1,25-dihydroxy vitamin D (1,25- (OH) 2 D). This second hydroxylation also occurs in other tissues such as bone, placenta, prostate, macrophages, lymphocytes, and colon cells.
From the same point of view, vit D still has an immunological role. Calcitriol increases phagocytosis and H2O2 secretion, which are important in the microbicidal and tumoricidal activity of macrophages. In addition, it reduces the production of pro-inflammatory cytokines, tumor necrosis factor-alpha, and production of anti-inflammatory drugs.
D3 supplementation helps to prevent some diseases directly and indirectly, such as hypocalcemia, also called milk fever. The doses of the vitamin that prevent milk fever are very close to the doses that can cause calcification.
Therefore, prevent other diseases, for example:
In short, vitamin D has many functions in the body, from calcium homeostasis to the modulation of the immune system. It also promotes optimal innate and adaptive immune function, which improves cows’ defenses against infections. Cows secrete a large amount of Ca into milk at the beginning of lactation, which leads to lactational osteoporosis. Therefore, they must replenish their bone reserves in the middle and at the end of lactation, which is aided by vitamin D supplementation. Because poor skeletal health or the inability to replenish there Ca reserves makes cows more vulnerable To subclinical hypocalcemia, which results in greater susceptibility to infections and other associated diseases. Finally, they promote the use of antimicrobials that can leave residues in milk and dairy products if not administered correctly.
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