Bone Resorption, Renal Function and Mineral Status in Cows Treated With 1,25-Dihydroxycholecalciferol and Its 24-Fluoro Analogues

: The relative potencies of 1,25-dihydroxycholecalciferol, 24-F-1,25-dihydroxycholecalciferol, and 24,24-F2-1,25-dihydroxycholecalciferol at three doses (25, 100 or 400 micrograms) were assessed in nonlactating Jersey cows. The 24,24-F2-1,25-dihydroxycholecalciferol induced a significantly greater hypercalcemia and hyperphosphatemia than did 1,25-dihydroxycholecalciferol. The 24-F-1,25-dihydroxycholecalciferol was intermediate in its hypercalcemic and hyperphosphatemic potency. Urinary hydroxyproline excretion rate and plasma hydroxyproline concentration were not significantly increased by treatment with any of the compounds. This indicates that these compounds did not stimulate bone resorption in nonlactating, nongravid cows. Renal function was significantly impaired in cows that received a 400-micrograms dose of any compound. There was a severe reduction in glomerular filtration rate (up to 42%) and urine specific gravity. Renal function was most severely affected in cows treated with 24,24-F2-dihydroxycholecalciferol and was evident even at the 100-micrograms dosage level.