Ravault J P, Pelletier J
C R Acad Sci III. 1986;303(14):629-31.
Adult rams were submitted to an artificial light regime with increasing and decreasing daylengths between 6 and 20 hrs. over a period of 8 months. Blood samples occurred at different durations of daylengths for measuring plasma levels of prolactin. Levels were high for a daily duration of light of 14.20, 17 and 18.30 hrs. along the increasing light-phase and of 18.30 hrs. during the decreasing light-phase. On the other hand prolactin levels were low for short daylengths, but also for a daylength of 20 hrs. It clearly appears that hyperlong days (greater than 18 hrs.) do not stimulate (or do actively inhibit) the secretion of prolactin in ovines.
成年公羊在8个月的时间里接受了一种人工光照制度，日照时长在6至20小时之间逐渐增加和减少。在不同的日照时长下采集血样，以测量血浆中催乳素的水平。在日照时长增加阶段，当日照时长为14.20、17和18.30小时时，催乳素水平较高；在日照时长减少阶段，日照时长为18.30小时时，催乳素水平也较高。另一方面，短日照时长时催乳素水平较低，但日照时长为20小时时催乳素水平同样较低。显然，超长日照（超过18小时）不会刺激（或实际上会抑制）绵羊催乳素的分泌。
