Malpaux B, Karsch F J
Reproductive Sciences Program, University of Michigan, Ann Arbor 48109-0404.
J Reprod Fertil. 1990 Nov;90(2):555-62. doi: 10.1530/jrf.0.0900555.
This study tested the hypothesis that short days can prolong the breeding season of the ewe when reproductive activity is initiated by an endogenous process, as opposed to when it is driven by exposure to short days. Suffolk ewes were ovariectomized and treated with Silastic capsules containing oestradiol; reproductive activity was monitored from serum concentrations of LH. In this model, a rise in LH is indicative of onset of the breeding season and the duration of the elevation in LH is an indicator of length of reproductive activity. The ewes were subjected to 6-month alternations between long and short photoperiods such that the LH rise began during exposure to the inhibitory long photoperiod (i.e. it resulted from an endogenous process). When short days were provided soon after such a spontaneous onset of the LH rise, the duration of reproductive activity was greater than that observed when ewes were maintained in long days throughout the LH elevation (194 +/- 10 vs 155 +/- 15 days; P less than 0.02). Since the transition from anoestrus to the breeding season in Suffolk ewes maintained outdoors does not require a decrease in daylength and appears to be generated by an endogenous process, our results support the hypothesis that shortening photoperiod sustains the natural breeding season which begins in early autumn.
当繁殖活动由内源性过程启动时，短日照可延长母羊的繁殖季节，这与繁殖活动由短日照暴露驱动的情况相反。对萨福克母羊进行卵巢切除，并使用含雌二醇的硅橡胶胶囊进行处理；通过血清促黄体生成素（LH）浓度监测繁殖活动。在该模型中，LH升高表明繁殖季节开始，LH升高的持续时间是繁殖活动时长的一个指标。母羊经历了6个月的长日照和短日照交替，使得LH升高在暴露于抑制性长日照期间开始（即它是由内源性过程导致的）。当在LH升高自发开始后不久提供短日照时，繁殖活动的持续时间长于母羊在整个LH升高期间处于长日照时观察到的持续时间（194±10天对155±15天；P<0.02）。由于在户外饲养的萨福克母羊从乏情期到繁殖季节的转变不需要日照长度的减少，且似乎是由内源性过程产生的，我们的结果支持了以下假设：缩短光照周期可维持始于初秋的自然繁殖季节。
