title: Physiological limit of the daily endogenous cholecalciferol synthesis from UV light in cattle.
abstract: The link between UV light (sunlight) and endogenous cholecalciferol (vitamin D3) synthesis in the skin of humans has been known for more than a 100 years, since doctors for the first time successfully used UV light to cure rickets in children. Years later, it was shown that UV light also had a significant effect on the cholecalciferol status in the body of cattle. The cholecalciferol status in the body is measured as the plasma concentration of 25-hydroxycholecalciferol, which in cattle and humans is the major circulating metabolite of cholecalciferol. Very little is, however, known about the quantitative efficiency of UV light as a source of cholecalciferol in cattle nutrition and physiology. Hence, the aim of this study was to determine the efficiency of using UV light for increasing the plasma 25-hydroxycholecalciferol concentration in cholecalciferol-deprived cattle. Twelve cows deprived of cholecalciferol for 6 months were divided into three treatment groups and exposed to UV light for 30, 90 or 120 min/day during 28 days. UV-light wavelengths ranged from 280 to 415 nm and 30-min exposure to the UV light was equivalent to 60-min average summer-sunlight exposure at 56 °N. Blood samples were collected every 3-4 days and analysed for 25-hydroxycholecalciferol and cholecalciferol. Results showed that increasing the exposure time from 90-120 min/day did not change the slope of the daily increase in plasma 25-hydroxycholecalciferol. Hence, it appears that cholecalciferol-deprived dairy cattle are able to increase their plasma 25-hydroxycholecalciferol concentration by a maximum of 1 ng/ml/day from UV-light exposure.
authors.affiliation: Department of Animal Science, Aarhus University, Tjele, Denmark.
authors.forename: L
authors.initials: L
authors.lastname: Hymøller
authors.affiliation: Department of Animal Science, Aarhus University, Tjele, Denmark.
authors.forename: S K
authors.initials: SK
authors.lastname: Jensen
authors.affiliation: SR Light aps, Herning, Denmark.
authors.forename: P
authors.initials: P
authors.lastname: Kaas
authors.affiliation: National Food Institute, Technical University of Denmark, Søborg, Denmark.
authors.forename: J
authors.initials: J
authors.lastname: Jakobsen
mesh_terms: D000818:Animals; D002112:Calcifediol / Q000097:blood* / Q000378:metabolism; D002417:Cattle / Q000378:metabolism*; D002762:Cholecalciferol / Q000096:biosynthesis*; D004307:Dose-Response Relationship, Radiation; D010858:Pigmentation; D012867:Skin / Q000378:metabolism* / Q000528:radiation effects; D014466:Ultraviolet Rays
chemical_list: D002762:Cholecalciferol; D002112:Calcifediol
keywords: cattle; cholecalciferol; endogenous; excretion; milk; repletion