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Relative Concentration of Extrogen and Progestrone in Milk and Blood, and Excretion of Estrogene in Urine¹

Purdue University, West Lafayette, IN 47907

Abstract

Concentrations of progesterone, estrone, estradiol-17/ß and estradiol-17 in prepartum mammary secretions and in milk of cows were indicative of concentrations of these steroids in plasma. Rates of excretion of estrogens in urine reflected concentrations of the estrogens in milk and blood plasma. Concentrations of progesterone in mammary secretions first exceeded concentrations in blood plasma about 5 days prior to calving and may be up to fourfold higher in milk (up to 30 ng/ml) than in blood plasma during lactation. However, compared to daily production rates or to transfer of radioactivity from progesterone, only .06 to .25% of progesterone is excreted in milk. Concentrations of estrogens in milk of untreated cows (3 to 25 days of lactation) averaged (pg/ml) 28 ± 2, 13 ± 1, 160 ± 14, and 202 ± 15 for estrone, estradiol-17/ß, estradiol-17, and total estrogen, respectively. In comparison, concentrations in colostrum on day of calving were 65- to 80-fold higher for estradiol-17/ß and estrone, and eightfold higher for estradiol-17. Compared to concentrations in blood plasma, concentrations of estradiol-17/ß in mammary secretions were higher prepartum and lower during early lactation, estrone was lower both prepartum and postpartum, and estradiol-17 was lower prepartum but several times higher during early lactation. From 3 to 25 days of lactation, biologically inactive estradiol-17 represented at least 70% of the total estrogen in milk as it does at nearly all times in cow urine. Total estrogen excreted in milk of cows was inversely proportional to its rate of excretion into urine. The proportions of estrogen excreted in milk varied from 2.6% to .03% for lowest to highest rates of urinary excretion of estrogen. These amounts would be about threefold less (.87 to .004%) if based on total estrogen excreted in urine and feces.

¹ Journal paper No. 6479, Purdue University Agricultural Experiment Station. Presented as part of the symposium on Natural Hormones in Edible Animal Products held during the A.S.A.S. meeting at Texas A&M University, August 16, 1976. Publication supported in part by DHEW/PHS/FDA/BVM contract No. 221-76-0129.

² Department of Animal Sciences

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