Serum Luteinizing Hormone (LH) in Ewes Treated with Various Dosages of 17β-Estradiol at Three Stages of the Anestrous Season2

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Abstract
THIRTY mature Columbia ewes, averaging 80 kg body weight, were divided randomly into six equal treatment groups. Each treatment consisted of a single intramuscular (im) injection of either 0, 12.5, 25, 50, 100 or 200 µg of 17β-estradiol (E2) in 1 ml of safflower oil. Blood samples were collected immediately preceding E2 treatment and at 3-hr, intervals for 27 hr. post-treatment. The same E2 treatment was administered to each ewe at three different times during the anestrous season: early (May 7), mid (June 21) and late (August 5). Estrus was monitored by a vasectomized ram from May 5 until 1 month after the last treatment. None of the ewes exhibited estrus until 4 days after the late anestrous treatments. Serum samples were assayed by a validated double antibody radioimmunoassay for ovine LH. There were no differences (P> .05) between the mean serum LH concentrations before the oil control injection and the mean of the highest LH concentrations after the oil injection. The ewes treated with 12.5 pg E2 or more exhibited a surge of serum LH 12 to 18 hr. after treatment. The mean peak LH concentrations of the 12.5 through the 200 µg E2 treated groups were all greater (P<.01) than the mean of the highest LH concentrations of the oil treated controls. The peak LH concentration of the 12.5 µg group was lower (P<.05) than the other E2 treated groups. The mean concentration of the LH peaks for all doses of E2 was 52.8 ng/ml (NIH-LH-S16). Not all of the E2 injections administered elicited a response in the form of an elevated serum LH concentration. The percentage of ewes responding to the oil, 12.5, 25, 50, 100 and 200 µg E2 groups were 0% (0/ 15), 67% (10/15), 87% (13/15), 93% (14/15), 93% (14/15), and 93% (14/15), respectively. There were no differences (P>.05) in the mean LH peak concentrations among any of the three anestrous stages. The late anestrous E2 treatment resulted in larger variations in the height of the LH response than did the early or mid anestrous treatments. The time lapse between the E2 treatment and the peak LH concentration was not affected by either the E2 dose or the anestrous stage. There was no dose response relationship between LH release and treatment with dosages of E2 between 12.5 and 200 µg. Copyright © 1973. American Society of Animal Science . Copyright 1973 by American Society of Animal Science.

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