The effect of 1 alpha-hydroxycholecalciferol on the concentrations of calcium, magnesium and inorganic phosphate in the plasma of parturient cows.

Abstract

135 Cows which were expected to produce a second or subsequent calf within 4--11 received an intramuscular injection of 500 micrograms 1 alpha-hydroxycholecalciferol (1 alpha-OHD3). In those animals in which the interval between injection and calving was at least 7 d there was, at 7 d after injection of 1 alpha-OHD3, a significant increase (P less than 0.001) in the blood plasma concentrations of Ca and Pi and a significant reduction (P less than 0.05) in that of Mg, compared with those in control animals. Within 24 h of calving there was a significant increase (P less than 0.001) in the concentration of Pi but no change in Ca or Mg compared with pre-injection levels, whilst the control animals showed a significant fall (P less than 0.001) in the concentration of Ca and a rise in those of Pi (P less than 0.001) and Mg (P less than 0.05). There was a significant reduction (P less than 0.001) in the number of animals with hypocalcaemia (defined as a plasma Ca concentration less than 1.9 mmol/l) in all animals injected with 1 alpha-OHD3; this reduction was particularly marked when the interval between injection and calving was between 1 and 8 d. The previously reported reduction in the incidence of clinical milk fever is considered to be a consequence of the effect of 1 alpha-OHD3 on the concentration of Ca in plasma.