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BOR - Papers in Press, published online ahead of print November 21, 2007.
Biol Reprod 2007, 10.1095/biolreprod.107.064394
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biolreprod.107.064394v1
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BIOLOGY OF REPRODUCTION 78, 552–562 (2008)
DOI: 10.1095/biolreprod.107.064394
© 2008 by the Society for the Study of Reproduction, Inc.

Endogenous Circannual Cycles of Ovarian Activity and Changes in Prolactin and Melatonin Secretion in Wild and Domestic Female Sheep Maintained under a Long-Day Photoperiod1

Amelia Gómez-Brunet 2 3, Julián Santiago-Moreno 3, Ana del Campo 3, Benoit Malpaux 4, Philippe Chemineau 4, Domingo J. Tortonese 5, Antonio Gonzalez-Bulnes 3, and Antonio López-Sebastián 3

Departamento de Reproducción Animal,3 Instituto Nacional de Investigaciones Agrarias, SGIT-INIA, 28040 Madrid, Spain Physiologie de la Reproduction et des Comportements,4 UMR 6175, INRA-CNRS-Université de Tours-Haras Nationaux, 37380-Nouzilly, France Department of Anatomy,5 University of Bristol, Bristol BS2 8EJ, United Kingdom

ABSTRACT

The present study examines the ovulatory activity of wild and domesticated ewes subjected to either a constant photoperiod of long days (16L:8D) or natural changes in daily photoperiod for 16 mo. The aim was to determine whether an endogenous reproductive rhythm controls seasonal reproductive activity in these sheep, and how the photoperiod might affect this. The effects of long-day photoperiods on long-term changes in prolactin and melatonin secretion were also evaluated. The two species showed changes in reproductive activity under the constant photoperiod conditions, suggesting the existence of an endogenous rhythm of reproduction. This rhythm was differently expressed in the two types of ewe (P < 0.05), with the domestic animals exhibiting much greater sensitivity to the effects of long days. A circannual rhythm of plasma prolactin concentration was also seen in both species and under both photoperiod conditions, although in both species the amplitude was always lower in the long-day animals (P < 0.01). The duration of the nocturnal melatonin plasma concentrations reflected the duration of darkness in both species and treatments. The peak melatonin concentration did not differ between seasons either under natural or long-day photoperiods.

melatonin, ovarian cycles, ovulatory cycle, photoperiod, prolactin, seasonal reproduction, wild and domestic ewes

FOOTNOTES

1Supported by grant PB-0435 from the Spanish DGICYT.

Correspondence: 2FAX: 34 91 347 4014; e-mail: gomez{at}inia.es






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Copyright © 2008 by the Society for the Study of Reproduction.