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BOR - Papers in Press, published online ahead of print January 3, 2007.
Biol Reprod 2007, 10.1095/biolreprod.106.057406
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BIOLOGY OF REPRODUCTION 76, 673–680 (2007)
DOI: 10.1095/biolreprod.106.057406
© 2007 by the Society for the Study of Reproduction, Inc.

research-article

Differential Estradiol Requirement for the Induction of Estrus Behavior and the Luteinizing Hormone Surge in Two Breeds of Sheep1

S. Ben Saïd , D. Lomet , D. Chesneau , L. Lardic , S. Canepa , D. Guillaume , C. Briant , C. Fabre-Nys , and A. Caraty 2

UMR Physiologie de la Reproduction et des Comportements, INRA/CNRS/Université Tours/Haras Nationaux, 37380 Nouzilly, France

ABSTRACT

For a better understanding of the mechanisms that lead to the preovulatory GnRH/LH surge and estrus behavior, the minimum estradiol (E) requirements (dose and duration) to induce each of these events were determined and compared between two breeds of ewes having either single (Ile de France) or multiple (Romanov) ovulations. The ewes were initially studied during a natural estrus cycle, and were then ovariectomized and run through successive artificial estrus cycles. For these artificial cycles the duration and amplitude of the follucular phase E increase were manipulated by E implants. Under all conditions, the onset of estrus behavior was similar in the two breeds, although its duration was longer in Romanov ewes. While a moderate E signal (6 cm for 12 h) induced an LH surge in 10/10 Ile de France ewes, a larger E signal (12 cm for 12 h) was minimally effective in Romanov ewes (4/10). Additional studies revealed that a small E signal (3 cm for 6 h) induced full estrus behavior in all Romanov ewes but was completely ineffective in Ile de France animals (0/10). Higher doses and mostly longer durations of the E signal (12 cm for 24 h) were required to induce a surge in all the Romanov ewes. These results demonstrate a clear difference in the E requirement for the induction of estrus behavior and the LH surge between breeds of ewes that have different ovulation rates. These data provide compelling evidence that, in one breed, the neuronal systems that regulate both events require different estrogen signals.

ewes, hypothalamus, ovulation, pituitary, sexual behavior

FOOTNOTES

1Supported by ACI Technologie.

Correspondence: 2FAX: 33 24 742 7743; e-mail: caraty{at}tours.inra.fr






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Copyright © 2007 by the Society for the Study of Reproduction.