Influence of UVB exposure on the vitamin D status and calcium homoeostasis of growing sheep and goats.

The purpose of this study was to investigate the influence of exposure to ultraviolet radiation (UVB) on vitamin D status, intestinal calcium absorption and bone metabolism in growing sheep and goats. The hypothesis was that growing sheep and goats are able to synthesise vitamin D within their skin as a result of UVB exposure and that respective consequences for their vitamin D blood levels and the associated parameters can be shown. Fourteen 18-week-old lambs and goat kids were kept in an UVB-free environment and randomly assigned to two groups. One group was daily exposed to UVB (300 watt) for 12 weeks, and the other served as a control group. Except for the exposure to UVB, all animals were kept under the same conditions and fed according to their requirements. Before the start of the experiment and every second week, blood samples were taken. Also the left metatarsus of each animal was analysed by quantitative computer tomography to test for bone mineral status before the start, in week 7 and at the end of the experiment. After 12 weeks, the animals were slaughtered and samples were taken from skin, gastrointestinal tract and kidney for further analyses. In this study, exposure to UVB led to increased serum 1,25-dihydroxyvitamin D (1,25VitD) levels in goat kids, whereas in lambs, serum 25-hydroxyvitamin D (25VitD) levels were increased. In both species UVB-exposed animals showed lower 7-dehydrocholesterol (7DHC) values in skin than their respective control groups. These results indicate that growing goat kids and lambs are able to synthesise vitamin D in the skin when being exposed to UVB.