Prevention of parturient hypocalcemia: effect of a single oral dose of 1,25-dihydroxyvitamin D3.

Norwegian Red cows 4 yr or older were fed a high calcium diet the last 2 to 4 wk before calving to increase the severity of hypocalcemia at parturition. An oral dose of pellets of fat-encapsulated 1,25-dihydroxyvitamin D3 (500 micrograms) was given to 15 cows and placebo pellets to 12 cows. Treated cows were grouped according to time of treatment, 1) 4 cows treated within 24 h of calving, 2) 8 cows treated 1 to 3 days before, and 3) 3 cows treated 4 to 5 days before calving. Minerals in blood plasma were measured from day -10 to day +10 (calving: day 0). Average calcium concentration of cows treated 1 to 3 days before calving decreased from 2.6 to 2.4 and of placebo treated from 2.5 to 1.8 mmol/liter from day -1 to day +1. Treatment with 1,25-dihydroxyvitamin D3 at other times did not protect against hypocalcemia. Average concentrations of 1,25-dihydroxyvitamin D in plasma were 200 to 250 pg/ml on days -2 and -1 in 5 cows treated on days -3 and -2. Similar concentrations were reached by placebo cows 1 to 2 days after parturition. A single oral dose of 500 micrograms 1,25-dihydroxyvitamin D3 given 1 to 3 days before parturition can prevent hypocalcemia at calving. Difficulties in judging actual time for parturition led to optimal treatment of only 8 of 15 cows.