METABOLISM OF VITAMIN D IN DOMESTIC ANIMALS

Vitamin D se pojavljuje u dva oblika. Vitamin D2 ili ergokalciferol nalazimo u biljkama, dok vitamin D3 ili kolekalciferol nalazimo u životinjskom organizmu. Životinje su sposobne sintetizirati vitamin D3 pomoću sunčevih ultraljubičastih zraka. Tijekom izlaganja sunčevoj svjetlosti, visokoenergetski ultraljubičastifotoni prodiru kroz epidermis i fotoliziraju provitamin 7-dehidrokolesterol nakon čega nastaje predvitamin D3. 7-dehidrokolesterol je derivat kolesterola i prirodno se nalazi u koži životinja i ljudi. Nastali predvitamin D3 prolazi kroz termički induciranu izomerizaciju i na taj način prelazi u biološki aktivan oblik vitamina D3. Aktivni oblik vitamina D3 ulazi u krvotok i odlazi u jetru gdje hidroksilacijom nastaje 25-OH vitamin D, te kao takvoga ga globularni prijenosnici vitamina D prenose u bubrege gdje pomoću multifunkcionalne monooksigenaze nastaje 1,25-(OH)2 vitamin D3 (kalcitriol) ili hormonski oblik vitamina D3. Hormonski oblik vitamina D odlazi u crijeva i kosti gdje mu je najvažnija funkcija reguliranje metabolizma kalcija i fosfora. Vitamin D se također može primiti i pomoću hranidbe (ergokalciferol). Od biljnih krmiva, ergokalciferolom su bogata voluminozna krmiva poput sijena lucerne, crvene djeteline, silaže lucerne i ječma i sl., a od životinjskih krmiva (kolekalciferol) različita ulja tune, bakalara, sabljarke, itd. Višak vitamina D u organizmu domaćih životinja je rijetka pojava zbog dobre regulacije. Nedostatak vitamina D dovodi do rahitisa, zaostajanja u rastu, učestalih prijeloma, te erozija raznih zglobova.There are two forms of vitamin D. Vitamin D2 or ergocalciferol can be found in plants while vitamin D3 or colecalciferol have presence in animal organism. Animals are able to synthesize vitamin D3 by ultraviolet sunlight. During exposure to sunlight, high-energy ultraviolet photons penetrate trough epidermis and photolyse provitamin 7-dehydrocholesterol and the previtamin D3 is created. 7-dehydrocholesterol is a cholesterol derivative and normally can be found in animal and human skin. Created previtamin D3 undergoes termally induced isomerization and thus become biologically active form of vitamin D3. That active form enters the blood stream to the liver where runs trough hydroxylation and 25-OH vitamin D occurs. 25-OH vitamin D travel to kidney via globular carriers where 1,25-(OH)2 vitamin D3 (calcitriol) or hormonal form of vitamin D3 occurs using multifunctional monooxygenase. After that hormonal form of vitamin D travel to digestive tract and bones where its lead role is regulation metabolism of calcium and phosphorus. Also, vitamin D can be taken by feed (ergocalciferol). Among plant fodder, high concetration of ergocalciferol can be found in voluminous fodders like alfalfa hay, red clover, alfalfa silage and barley, etc. In animal feedstuff (colecalciferol) various fish oils like tuna oil, cod, swordfish, etc. Excess of vitamin D in animal organism is rare because of good regulation. Defiance of vitamin D leads to rickets, growth retardation, frequent fractures and joint erosions