J. Anim Sci.
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J. Anim Sci. 1984. 58:409-415.
© 1984 American Society of Animal Science
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Testosterone Effects on Gonadotropin Response to GNRH: Cows and Pony Mares1

D. L. Thompson, Jr., S. A. Voelkel, S. I. Reville-Moroz, R. A. Godke and D. J. Derrick

Louisiana State University2, Baton Rouge 70803

Abstract

Effects of testosterone propionate (TP) treatment on plasma concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) before and after an injection of gonadotropin releasing hormone (GnRH) were studied using ovariectomized cows and pony mares. An initial injection of GnRH (1 µg/kg of body weight) was followed by either TP treatment or control injections for 10 (cows) or 11 (ponies) d. A second GnRH injection was administered 1 d after the last TP or oil injection. Concentrations of LH and FSH were determined in samples of plasma taken before and after each GnRH injection. Control injections did not alter the response to GnRH (area under curve) nor the pre-GnRH concentrations of LH and FSH in ovariectomized cows or ponies. Testosterone treatment increased (P<.01) the FSH release in response to GnRH in ovari-ectomized mares by 4.9-fold; there was no effect in cows, even though average daily testosterone concentrations were 59% higher than in pony mares. Testosterone treatment reduced the LH release in response to GnRH by 26% in ovariectomized mares (P<.05) and by 17% in ovariectomized cows (P=.051). These results are consistent with a model that involves ovarian androgens in the regulation of FSH secretion in the estrous cycle of the mare, but do not support such a model in the cow.

Footnotes

1 Portions of these data were used in partial fulfillment of requirement for the degree of Master of Science by S. I. Reville-Moroz. We thank C. A. Johnson, M. C. Schiewe and M. P. Walker for their technical assistance.

2 Dept. of Anim. Sci., Louisiana Agr. Exp. Sta., Louisiana Stata Univ. Agr. Center.






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Copyright © 1984 by the American Society of Animal Science.