Influence of an alimentary supplementation with 25-hydroxycholecalciferol on ovine calcium homeostasis

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Peripartal hypocalcemia is a common problem in dairy cows. Although hypocalcemic animals do not always develop clinical milk fever, the transient decrease in plasma calcium concentration predisposes the animals towards various health problems and diseases. Recently, our group could demonstrate that the oral supplementation with the vitamin D metabolite 25-hydroxycholecalciferol could be a promising concept to stabilize peripartal calcium homeostasis. As the mentioned study was carried out in a commercial dairy herd, the facilities to characterize the mechanisms mediating the observed physiological effects were limited. The herewith submitted project is designed to determine the effects of 25-hydroxycholecalciferol on the gastrointestinal tract, the kidney and the skeleton, the organs which are crucial for the regulation of calcium homeostasis. Sheep will be used as an animal model for the investigations which include in vivo-balance studies as well as functional and structural studies focusing on the epithelial and cellular level. Taking advantage of an animal experiment carried out under standardized conditions we hope to verify our hypotheses on the putative effects of 25-hydroxycholecalciferol in order to obtain basic information necessary to develop an innovative concept to stabilize peripartal macromineral homeostasis in dairy cows.