Biochemical indicators of bone metabolic activity in bovine periparturient hypocalcemia.

Twenty-one paretic and 30 nonparetic periparturient ambulatory cows were studied together with 13 non-pregnant control cows. Blood samples were collected during a time period of 6 hours before or after parturition and from nonpregnant cows. A severe hypocalcemia (-44%) and hypophosphatemia (-69%) were found in the paretic vs. nonparetic periparturient animals, whereas serum magnesium concentrations were not altered. Serum alkaline phosphatase activity was modestly (-12%) but not significantly decreased in the paretic vs. nonparetic periparturient cows. Serum osteocalcin concentrations, which reflect osteoblast activity, were strikingly low during the periparturient period and more in the paretic cows but the difference between the paretic (-36%) and nonparetic animals was not statistically significant. In the paretic cows, serum 1,25-dihydroxyvitamin D concentrations were significantly increased (+53%) and those of hydroxyproline decreased (-18%) compared with the nonparetic animals. Serum estradiol levels were markedly increased in the periparturient vs. nonpregnant cows and more in the paretic animals, but, again, the difference between the paretic (+47%) and nonparetic animals was not statistically significant. Serum retinol concentrations were significantly lower (-18%) in the paretic vs. nonparetic periparturient cows probably reflecting increased lactation in the paretic animals. Collectively, the results indicate very low bone metabolic activity in the periparturient vs. nonpregnant cows and support the hypothesis of both osteoblast and osteoclast functions being impaired in the paretic animals.