VITAMIN-D STATUS AND HYPOCALCEMIC RESPONSE TO PROTAMINE IN EXERCISED AND NON-EXERCISED DAIRY-COWS

Bone resorption was studied in post parturient cows using intravenous injection of protamine. Protamine inhibits bone resorption and the pro tamine-induced hypocalcemia can be taken as a measure of this process. The studies were performed in a herd where half of the cows had been tied indoors for 2 1/2 years, the other half had been given daily exer cise during the same period. All animals were fed in the same way The hypocalcemic response to protamine was the same in both groups, which indicates that exercise did not change bone resorption. The serum leve ls of calcium, inorganic phosphorus and magnesium around parturition d id not differ. The daily exposure to daylight increased the serum leve l of 25-(OH)-cholecalciferol in late summer in the exercised group.