| Abstract: | The pattern of estrogen during four reproductive states of the cow was determined by utilizing a frequent blood sampling technique. Plasma samples from a Holstein heifer at thirty minute intervals were analyzed for estrone and estradiol-17 concentrations on day 218 of gestation, day 3 postpartum, day 12 postpartum, and day 10 of the first postpartum estrous cycle using a radioimmunoassay procedure. On day 218 of gestation two peaks in plasma estrone concentration occurred at a nine hour interval, while plasma estradiol-17 peaks were of smaller magnitude and greater frequency. On day 3 postpartum, mean plasma concentration of both steroids had decline and exhibited less variation. Mean plasma estradiol-17  concentration on day 12 postpartum was twice the concentration observed on day 10 of the estrous cycle. Mean concentration ratio of estrone to estradiol-17 was approximately 4:1 on day 218 of gestation and 25:1 on day 3 postpartum. These results indicate that a frequent sampling interval is neccesary for determining the circulating estrogen status in the bovine. Also, the significance of episodic plasma estrogen peaks may be related to pituitary gonadotrophin release and the estrone:estradiol17 ratio may be indicative of the reproductive status of the cow. |
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