Plasma levels of copper, iron and zinc during the estrous cycle of the ewe.

Serum levels of copper, iron and zinc were determined throughout complete estrous cycles in 16 ewes. All ewes were normally cycling females exhibiting normal serum progesterone patterns. Copper serum levels tended to be higher during the preovulatory and ovulatory times, presumably due to the transfer of hepatic celuloplasmin as a result of the release of endogenous estrogen. Iron and zinc plasma levels were higher during estrous when the ovarian tissue requirement was higher. It is suggested that the control mechanism responsible for the variations in copper, iron and zinc plasma levels during the estrous cycle may be hormonal in nature.