Seasonality of breeding in the ewe is controlled primarily by the length of the dark phase of the 24-hour day. Melatonin levels increase during this dark phase. The daily length of time of elevated melatonin secretion appears to be the trigger that signals the normal fall breeding season. Various light-dark regimens have resulted in varied estrous response. A treatment of 8 hours of light and 16 hours of dark (8L:16D) has, in general given the best response. Administration of exogenous melatonin should mimic the natural secretion associated with the extended dark phase. This study examined the effectiveness of light control or melatonin administration to induce cyclic reproductive activity during July and August.
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South Dakota State University
Copyright © 1989 South Dakota State University
Slyter, A. L. and Weiskircher, Kelly, "Lambing Performance of Ewes Treated with Melatonin of Artificial Photoperiod" (1989). South Dakota Sheep Field Day Proceedings and Research Reports, 1989. 1.