Effects of hypocalcaemia on blood flow to the ovaries of the sheep.

The objectives of the study were to use sheep as a model to determine whether a reduction in plasma calcium concentration similar to that observed during periods of postpartum subclinical hypocalcaemia in lactating dairy cattle might affect the blood flow to the ovaries. Different levels of hypocalcaemia were induced in each of six, non-pregnant sheep by the slow intravenous infusion of Na2-EDTA. Measurements of blood flow to the ovaries were made before and after the induction of hypocalcaemia, using 113Sn and 46Sc radiolabelled microspheres. As plasma ionized calcium was reduced, there was a significant decline in ovarian blood flow. Ovarian blood flow (percentage of resting) = 0.54 Ca++ (percentage of resting) + 58.4. This model was significant at P < 0.01, with R2 = 0.92. Accordingly, a reduction in plasma ionized calcium of 50% would yield a reduction in ovarian blood flow of 16%.