J. Anim Sci.
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J. Anim Sci. 1965. 24:986-989.
© 1965 American Society of Animal Science
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Alteration of Ovarian Activity in Cycling Beef Heifers with Small Daily Injections of Estradiol1, 2,

G. D. Niswender3, C. C. Kaltenbach3, R. P. Shumway4, J. N. Wiltbank5 and D. R. Zimmerman6

U. S. Department of Agriculture and University of Nebraska, Lincoln

Abstract

Daily injections of 20, 40, 80, 160, 320 or 640 mcg. of estradiol-17ß were administered to cycling beef heifers beginning on day 6 of the estrous cycle. Corpus luteum weight, progestin content, progestin concentration and follicular fluid weight at day 12 tended to be lower in the heifers injected with the higher levels of estrogen than in the control heifers. Similar estrogen treatment given daily from days 6 to 18 reduced luteal and follicular activity. Heifers receiving the higher levels of estradiol showed the greatest reduction.

There was no evidence obtained in this study to support the hypothesis that low levels of estrogen have a differential effect on the hypophysis of the heifer. In general, all levels of estrogen administered reduced all measures of ovarian activity taken and in no case was a stimulation of ovarian activity apparent.

Footnotes

1 Published with the approval of the Director as paper No.1669, Journal Series, Nebraska Agricultural Experiment Station.

2 This investigation was supported in part by PHS research grant (A-5665) from the National Institute of Child Health and Human Development, Public Health Service.

3 Present address: Department of Animal Science, University of Illinois, Urbana, Illinois.

4 Present address: Department of Animal Science, Brigham Young University, Provo, Utah.

5 Animal Husbandry Research Division, ARS, U.S.D.A., Fort Robinson Beef Cattle Research Station, Crawford, Nebraska,

6 Department of Animal Science, University of Nebraska, Lincoln, Nebraska.






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