SYMPOSIUM - CALCIUM-METABOLISM AND UTILIZATION - CALCIUM AND VITAMIN-D METABOLISM IN THE DAIRY-COW

Most dairy cows experience some degree of hypocalcemia during the peri parturient period. There is, however, a subgroup of dairy cows that ex perience a breakdown in their ability to maintain plasma calcium and, consequently, suffer, from severe hypocalcemia. This condition is also known as milk fever and usually occurs in cows in their third or grea ter lactation. The precise metabolic lesions responsible for the onset of milk fever have not yet been defined. Research has shown that milk fever is not the result of inadequate production of calcitropic hormo nes (parathyroid hormone and 1,25-dihydroxyvitamin D), but rather is m ore likely a result of inadequate receptor numbers or receptor dysfunc tion in the target cell of these hormones. This report reviews vitamin D and calcium metabolism, giving emphasis to 1,25-dihydroxyvitamin D receptor regulation and function as related to the periparturient dair y cow. The report also focuses on providing insights into nutritional (anionic diets) and endocrine strategies that have proved useful in mi lk fever management.