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

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.

Effect of intravaginal fluorogestone acetate sponges on prolactin levels of Damascus-local cross breed goats

“…Teleb et al (2003) reported that PRL levels in Damascus goats were significantly higher during the non-breeding season (MarchMay) and tend to decrease as the breeding season (JuneNovember) approaches. An inverse relationship between PRL levels and reproductive activity in sheep and goats has also been reported by Gomez-Brunet et al (2008), Hesselink et al (1995), and Mori et al (1985). A significant increase in PRL levels following insertion and withdrawal of the intravaginal fluorogestone acetate sponges in all goat groups was demonstrated in this study.…”

Sexually active males prevent the display of seasonal anestrus in female goats

“…It is a mixed breed resulting from crosses between various seasonal European breeds. It displays marked breeding seasons of about 6 month duration, with a circannual reproductive endogenous rhythm independent of food availability (Aguilar et al, 2001;Duarte et al, 2008), as reported in others breeds of sheep and goats from temperate latitudes (Gómez-Brunet et al, 2008;Karsch et al, 1989). Furthermore, it shows "classical" reproductive responses to short days and to long days, as well as existence of periods of refractoriness to long days and to short days (Delgadillo et al, 2011;Duarte et al, 2010), as in Saanen dairy goats (Gebbie et al, 1999).…”

Prolactin and the physiological regulation of its secretion. A review

“…This phenomenon is especially evident in seasonally breeding species. In sheep, the short day photoperiod, elevates plasma melatonin concentration which in turn leads to the inhibition in the secretion of PRL (Misztal et al, 1997;Morgan, 2000;Molik et al, 2007;Gomez-Brunet et al, 2008;Morgan and Hazlerigg, 2008;. Numerous data indicated that prolonged treatment with melatonin (i.e.…”