Robinson J E, Karsch F J
AFRC Institute of Animal Physiology and Genetics Research, Babraham, Cambridge, England.
Reprod Nutr Dev (1980). 1988;28(2B):365-74. doi: 10.1051/rnd:19880303.
Photoperiod is the proximate cue which times the reproductive period of the sheep and the role of daylength as a "zeitgeber" is evaluated in this report. Although sheep are regarded as a short-day breeding species, the reproductive period of the Suffolk ewe begins on daylengths which are on average 2.5 hours longer than those on which it ends. The reasons for this apparent anomaly are considered. Experimental evidence is presented which demonstrates that the transitions between the breeding season and anoestrus are not actively generated by changing ambient photoperiod. Rather the ewe expresses an endogenous circannual rhythm of reproduction and the role of daylength is to entrain this reproductive rhythm to a period of 365 days. It appears that only portions of the annual cycle of photoperiod are necessary to synchronize the breeding season, however, additional photic cues may be required to produce a reproductive period of normal duration.
光照周期是调节绵羊繁殖期的直接线索，本报告评估了日长作为“授时因子”的作用。尽管绵羊被视为短日照繁殖物种，但萨福克母羊的繁殖期开始时的日长平均比结束时的日长长2.5小时。本文探讨了这一明显异常现象的原因。实验证据表明，繁殖季节和乏情期之间的转变并非由环境光照周期的变化主动引发。相反，母羊表现出一种内源性的年繁殖节律，日长的作用是将这种繁殖节律调整为365天的周期。然而，似乎只有一年中光照周期的部分时段对于同步繁殖季节是必要的，可能还需要额外的光信号来产生正常时长的繁殖期。
