THE EFFECT OF PARENTERALLY APPLIED 25-HYD ROXYCHOLECALCIFEROL AND 1-ALPHA-HYDROXYCHOLECALCIFEROL ON MINERAL CONCENTRATIONS IN THE BLOOD OF HEAVILY PREGNANT COWS

The effect of 1 - 3 intramuscular injections of the vitamin D3 metabol ite 25-OHD3, synthetic 1alpha-OHD3, and a combination of both on the p lasma concentrations of calcium (Ca), inorganic phosphate (P(i)) and m agnesium (Mg) was tested in 67 older dry dairy cows. Administering 4,0 mg 25-OHD3 reduced Ca and P(i) for some time while Mg blood levels re mained constant. Injecting 210 mug 1alpha-OHD3 plus 2,0 mg 25-OHD3 onl y brought a marked increase in P(i) concentrations, whereas 420 mug 1a lpha-OHD, plus 4,0 mg 25-OHD3, and 350 mug 1alpha-OHD, alone significa ntly raised Ca and P(i) levels beginning on the 2nd day after injectio n and lasting for at least 6 days. These higher levels can be maintain ed by repeated injections. Another effect of injecting 1alpha-OHD3 was to depress Mg blood levels, and a negative effect on the Ca and vitam in D3 metabolism is suggested wich may cause hypocalcaemia when the ef fect of 1alpha-OHD3 subsides. Metastatic calcifications of soft tissue s were observed in some 1alpha-OHD3-treated cows.