Submitted July 17, 2007
Returned for revision August 8, 2007
Accepted November 13, 2007
Neuroendocrinology
Endogenous Circannual Cycles of Ovarian Activity and Changes in Prolactin and Melatonin Secretion in Wild and Domestic Female Sheep Maintained under a Long-Day Photoperiod
Amelia Gómez-Brunet *,
Julián Santiago-Moreno ,
Ana del Campo ,
Benoit Malpaux ,
Philippe Chemineau ,
Domingo J. Tortonese ,
Antonio Gonzalez-Bulnes ,
and
Antonio López-Sebastián
* To whom correspondence should be addressed. E-mail: gomez{at}inia.es.
Abstract
The present study examines the ovulatory activity of wild and domesticated ewes subjected to either a constant photoperiod of long days (16 h light/day) or natural changes in daily photoperiod for 16 months. 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 a 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.
Key words:
Melatonin •
Ovulatory cycle •
Prolactin •
Seasonal reproduction
