Estrogen concentrations in bovine and porcine tissues

Using an estrogen antiserum that measures biologically active estrogen (estradlol‐17ß + estrone), a series of studies have been completed to describe the normal plasma levels of estrogen in cows and sows during various stages of reproduction. The levels are lower in the nonpregnant cow (< 25 pg/ml) than in most species. Only during late pregnancy are the levels easily assayed. The levels in the nonpregnant sow are 2–3 times greater than in the cow. In both species there is a preovulatory peak of estrogen that is responsible for estrus. Plasma estrogen concentrations were also determined after induction of multiple ovulations by exogenous gonadotropin (PMSG) in the cow and sow and after treatment of cows with either a progestin (MGA) or a prostaglandin (PGF ₂ α). (These two drugs have been used to synchronize estrus in the cow.) Estrogen levels rise greatly after treatment with PMSG but show little effect from MGA or PGF ₂ α. Data are also presented on the validation of an assay for E ₂ ß and E ₁ in beef tissue. Less than 20 pg of E ₂ ß and E ₁ was measured per gram bovine muscle tissue. Considerable effort must be expended to apply radioimmunoassay to the assay of estrogens in tissues.