The accretion of copper and of zinc by the foetuses of prolific ewes.

Abstract

1. The amounts of copper and zinc in the foetuses of ewes carrying from one to four lambs were measured at different stages of gestation and estimates were made of the amounts of these metals in their livers.2. The accretion of Cu and Zn could be described by growth equations of the Gompertz form, from which could be derived estimates of the instantaneous and fractional rates of deposition of these metals in the foetal body.3. Between the 80th and 144th day of gestation the instantaneous rates of deposition of the metals increased exponentially, and at the end of pregnancy were calculated to be 0.24 and 2.0 mg Cu and Zn/d respectively in the triplet lamb foetus. The corresponding total accretions were estimated to be 10 and 69 mg respectively.4. The fractional rates of live-weight gain and of deposition of Cu were similar and decreased at similar rates; that of Zn deposition decreased much more slowly.5. The proportion of whole-body Cu estimated to be in the liver was always greater than 50 %. The amount of Zn in the liver remained constant and contributed 72 % of the total body Zn at 80 d but only 8 % at 144d.6. The relative amounts of Cu and of Zn accrued per unit body-weight gain were not constant during the development of the foetus. As foetal numbers increased the amounts of each metal deposited in the foetus decreased more rapidly than did foetal weight.7. The results are discussed in relation to the demands for Cu and Zn during pregnancy in sheep.