Siopes T D
Department of Poultry Science, North Carolina State University, Raleigh 27695-7608, USA.
Poult Sci. 1998 Jan;77(1):145-9. doi: 10.1093/ps/77.1.145.
Two experiments were conducted to determine whether the critical day length (CDL) for photorefractoriness remained stable or varied by season of the year. The first experiment was done in the fall with photosensitive hens that were exposed to fixed day length treatments ranging from 12 to 16 h/d for 24 wk. At 24 wk of treatment, all hens were given 20 h light (L):4 h dark (D) and subsequent changes in egg production were used to evaluate photorefractoriness. This experimental approach was the same as that used by Siopes (1994) to estimate the CDL for photorefractoriness in winter-photostimulated hens. It was determined that the CDL for photorefractoriness in fall-photostimulated hens was 12 to 12.5 h, the same as that obtained in the earlier report for winter-photostimulated hens. A second experiment was done to further test the possibility that the CDL for photorefractoriness was static during the year. A gradually increasing photoperiod was started in winter at 12L:12D, just under the CDL for photorefractoriness but just over the CDL for egg production. Subsequent egg production and expression of photorefractoriness were compared to controls to estimate the dynamics of the CDL for photorefractoriness. Results supported a static CDL for photorefractoriness and suggest that any daily photoperiod exceeding 12 h will activate processes leading to photorefractoriness, independent of season.
进行了两项实验，以确定光不应性的临界日长（CDL）是保持稳定还是随年份季节变化。第一个实验在秋季进行，选用光敏母鸡，使其接受从12至16小时/天的固定日长处理，持续24周。在处理24周时，所有母鸡均给予20小时光照（L）：4小时黑暗（D），并通过随后产蛋量的变化来评估光不应性。该实验方法与Siopes（1994年）用于估算冬季光刺激母鸡光不应性CDL的方法相同。结果确定，秋季光刺激母鸡的光不应性CDL为12至12.5小时，与早期关于冬季光刺激母鸡的报告结果相同。进行了第二项实验，以进一步测试光不应性CDL在一年中是否保持不变的可能性。冬季从12L：12D开始逐渐增加光周期，刚好低于光不应性CDL，但略高于产蛋CDL。将随后的产蛋量和光不应性的表达与对照组进行比较，以估算光不应性CDL的动态变化。结果支持光不应性CDL保持不变的观点，并表明任何超过12小时的每日光周期都会激活导致光不应性的过程，与季节无关。
