The effect of intramuscularly administered vitamin D3 on serum vitamin D metabolites and electrolytes in vitamin D3 deficient dairy cows

The effect of intramuscular administration of vitamin D₃ (1×10⁶ IU D₃/100 kg bodyweight) to 3 different dairy breeds on the serum levels of vitamin D₃, 25-OH-D₂, 25-OH-D₃, Ca, inorganic P and Mg was studied.The vitamin metabolites and the electrolytes were analysed on 9 occasions during a 36-day period. Vitamin D₃ was analysed on 6 occasions during the same period. No significant breed differences were observed except for 25-OH-D₃ (P ≤ 0.05). The D₃ level rose in 1 day from < 2 ng/ml to 906 ng/ml and decreased to below 50 % of the peak level after 6 days. At the end of the experiment (day 36) vitamin D₃ was < 2 ng/ml. 25-OH-D₃ rose from < 2 ng/ml to 106 ng/ml in 6 days and stayed at this level during the whole experiment. 25-OH-D₂ decreased from 16 ng/ml to 5 ng/ml during the observation period.