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Timing of ovulations in the superovulated bovine
Authors:D.P. Maxwell  J.M. Massey  D.C. Kraemer
Affiliation:Department of Veterinary Physiology and Pharmacology Texas Agricultural Experiment Station Texas A&M University College Station, TX 77843 USA
Abstract:Plasma levels of estrone sulfate, estrone and estradiol, and progesterone were measured in six ewes throughout pregnancy. Estrone sulfate was detectable at around 70 days of gestation with values ranging between 0.3 – 0.7 pmol (0.1 – 0.3 ng) per ml. The level increased steadily to between 3 – 24 pmol (1 – 9 ng) per ml at about 2 days before lambing. An upsurge then followed reaching a maximal concentration between 40 – 130 pmol (15 – 50 ng) per ml. Unconjugated estrone and estradiol levels were appreciable only in the last 2–3 days of pregnancy and the profiles at this time followed closely that of estrone sulfate so that the molar ratio of estrone sulfate: estrone: estradiol remained remarkably constant at approximately 100:2:1 in spite of the great individual variations in absolute concentrations.The progesterone level was higher than that of estrone sulfate throughout pregnancy except 1–2 days prior to parturition. The sharp decline in progesterone concentration in the last two days coincided with the upsurge of estrone sulfate, but the net decrease in concentration was only about one-third of the net increase in estrone sulfate concentration during this period. These data are discussed in relation to the possible role of estrone sulfate and the possibility of placental conversion of progesterone to estrone sulfate during late pregnancy in the ewe.
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