ABSTRACT

The function of vitamin D in calcium homoeostasis in dairy cows, such as in other vertebrates, is known for many years. In recent years, new and interesting, non-classical functions of vitamin D have been elucidated, including effects on the immune system. The major aim of this review is to provide an overview of effects of vitamin D or its metabolites on the immune system in dairy cows. The first part of the review provides an overview of vitamin D metabolism, with particular reference to the role of various proteins (25- and 1-hydroxylases, vitamin D binding protein, vitamin D receptor) in vitamin D signalling. The second part deals with the role of the concentration of 25-hydroxyvitamin D [25(OH)D] in plasma as an indicator of the vitamin D status in dairy cows, and its dependence on sunlight exposure and dietary vitamin D supplementation. In this part also the “free hormone hypothesis” is discussed, indicating that the concentration of free 25(OH)D might be a more valid indicator of the vitamin D status than the concentration of total 25(OH)D. The third part deals with classical and the non-classical functions of vitamin D. Among the non-classical functions which are based on an autocrine vitamin D signalling, particular reference is given to the effects of vitamin D and vitamin D metabolites on the immune system in bovine immune cells and in dairy cows. Recent findings provide some indication that vitamin D or its metabolite 25(OH)D could enhance the immune function in dairy cows and be useful for the prevention and therapy of mastitis. However, the number of studies reported so far in this respect is very limited. Thus, much more research is required to yield clear concepts for an optimised usage of vitamin D to improve the immune system and prevent infectious diseases in dairy cows.

摘要

维生素 D 在奶牛（例如其他脊椎动物）体内钙稳态中的作用已为人们所知多年。近年来，已经阐明了维生素 D 的新的、有趣的、非经典的功能，包括对免疫系统的影响。本综述的主要目的是概述维生素 D 或其代谢物对奶牛免疫系统的影响。综述的第一部分概述了维生素 D 代谢，特别提到了各种蛋白质（25-和 1-羟化酶、维生素 D 结合蛋白、维生素 D 受体）在维生素 D 信号传导中的作用。第二部分涉及血浆中 25-羟基维生素 D [25(OH)D] 浓度作为奶牛维生素 D 状态指标的作用，以及它对阳光照射和膳食维生素 D 补充的依赖性。在这部分还讨论了“游离激素假说”，表明游离 25(OH)D 的浓度可能比总 25(OH)D 的浓度更有效地指示维生素 D 状态。第三部分涉及维生素 D 的经典和非经典功能。在基于自分泌维生素 D 信号传导的非经典功能中，特别提到了维生素 D 和维生素 D 代谢物对免疫系统的影响在牛免疫细胞和奶牛中。最近的研究结果表明，维生素 D 或其代谢物 25(OH)D 可以增强奶牛的免疫功能，有助于预防和治疗乳腺炎。然而，迄今为止在这方面报道的研究数量非常有限。因此，