Calcium effects on renal conservation of magnesium in cows

Urinary excretion rates for Ca, Mg and P were compared to simultaneous measurements of the same elements in blood plasma of cows recovering from moderate hypocalcaemia post partum and in 1 animal during recovery from hypocalcaemia induced by fasting.The renal conservation of Mg was found to be increased during the hypocalcaemia, theoretical tubular reabsorption rates being correlated to plasma Ca with r = –0.7, P < 0.001. The relationship was observed in the plasma Ca range from about 2.0 to 2.6 mmol/1.The findings may explain the occurrence of hypermagnesaemia in hypocalcaemic cows and the delay in the development of hypo-magnesaemia seen in cows with fasting-induced hypocalcaemia.