Effect of exogenous melatonin and extending the dark period at dusk before the summer solstice on the onset of oestrus in Romney Marsh ewes
Groups of Romney Marsh ewes ( n = 24) were injected with exogenous melatonin or subjected to extended darkness or a combination of both at dusk from the winter to the summer solstice before being re-exposed to the natural photoperiod at 35°S. The animals were at all times exposed to natural dawn. Th...
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Published in | Journal of reproduction & fertility Vol. 101; no. 1; pp. 145 - 150 |
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Main Authors | , , |
Format | Journal Article |
Language | English |
Published |
England
Society for Reproduction and Fertility
01.05.1994
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Subjects | |
Online Access | Get full text |
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Summary: | Groups of Romney Marsh ewes ( n = 24) were injected with exogenous melatonin or subjected to extended darkness or a combination of both at dusk from the
winter to the summer solstice before being re-exposed to the natural photoperiod at 35°S. The animals were at all times exposed
to natural dawn. The onset of subsequent oestrus was delayed when compared with controls subjected to the natural photoperiod.
Either melatonin or darkness or a combination were equally effective at delaying oestrus. The results are consistent with
a hypothesis based on an external coincidence model of seasonal breeding involving the coincidence of a light-sensitive phase
set close to dusk that, when exposed to light in spring and summer, prepares the reproductive axis to respond correctly to
the direct effects of the inductive photoperiod in autumn. The offset of the time of oestrus was not affected by the experimental
treatments nor was the timing of the subsequent reproductive season. Since melatonin was as effective as darkness at influencing
the assumed photosensitive signal, even in the presence of natural light, melatonin may act through the light reception system. |
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ISSN: | 1470-1626 0022-4251 1741-7899 |
DOI: | 10.1530/jrf.0.1010145 |