Siopes T D, Proudman J A
Department of Poultry Science, College of Agriculture and Life Sciences, North Carolina State University, Raleigh, North Carolina 27695-7608, USA.
Poult Sci. 2003 Jun;82(6):1042-8. doi: 10.1093/ps/82.6.1042.
Photosensitive species undergo neuroendocrine changes during a reproductive season that cause them to gradually become unresponsive to a photoperiod that initially stimulated reproduction. They may first become relatively photorefractory (rPR), when they will cease egg laying only if photoperiod is reduced, and then absolutely photorefractory (aPR), when they will cease laying despite long day length. Our objective was to test the photoresponsiveness of breeder turkey hens during egg production at various times following photostimulation and to relate photoresponsiveness to rPR and aPR as well as plasma levels of prolactin (PRL) and luteinizing hormone (LH). Hens were maintained in cages in light-controlled facilities and photostimulated at 31 wk of age (September) with a photoperiod of 16L:8D. At 8, 14, and 20 wk after photostimulation, treated hens received a 2-wk exposure to an 11.5L:12.5D photoperiod and were then returned to 16L:8D. Exposure to the shortened photoperiod at 8 wk of photostimulation resulted in three distinct responses of declining egg production: nonresponders (NR, 32.7% of hens), partial responders (PAR, 43.9%), or full responders (FR, 23.4%). Egg production returned to control levels following return to a 16L:8D photoperiod. This response repeated at the 14- and 20-wk treatment periods but with greater declines in egg production in the NR and PAR groups. The incidence of subsequent aPR in the NR, PAR, and FR groups was 5.7, 8.5 and 24%, respectively, as compared to 23.3% for the controls. Plasma LH and PRL concentrations also declined in response to 11.5L:12.5D and also rebounded following return to 16L:8D. The hormonal responses of NR, PAR, and FR were similar. We conclude that turkey hens exhibit varying degrees of rPR early during the egg laying season and that the incidence and severity of the rPR response increases as the laying season progresses. Further, PRL and LH levels did not reflect the differences in egg production among the responder and nonresponder groups to changes in photoperiod.
光敏物种在繁殖季节会经历神经内分泌变化，这会使它们逐渐对最初刺激繁殖的光周期不再产生反应。它们可能首先变得相对光不应性（rPR），此时只有在光周期缩短时才会停止产蛋，然后变为绝对光不应性（aPR），此时即使日照时间长也会停止产蛋。我们的目的是测试种火鸡母鸡在光刺激后的不同时间产蛋期间的光反应性，并将光反应性与rPR、aPR以及催乳素（PRL）和促黄体生成素（LH）的血浆水平联系起来。母鸡饲养在光照控制设施的笼子里，在31周龄（9月）时用16L:8D的光周期进行光刺激。在光刺激后的第8、14和20周，处理过的母鸡接受为期2周的11.5L:12.5D光周期照射，然后再回到16L:8D。在光刺激第8周时暴露于缩短的光周期导致产蛋量下降出现三种不同反应：无反应者（NR，占母鸡的32.7%）、部分反应者（PAR，占43.9%）或完全反应者（FR，占23.4%）。回到16L:8D光周期后，产蛋量恢复到对照水平。这种反应在第14周和第20周的处理期重复出现，但NR组和PAR组的产蛋量下降幅度更大。NR组、PAR组和FR组随后出现aPR的发生率分别为5.7%、8.5%和24%，而对照组为23.3%。血浆LH和PRL浓度也因11.5L:12.5D照射而下降，并在回到l6L:8D后反弹。NR组、PAR组和FR组的激素反应相似。我们得出结论，火鸡母鸡在产蛋季节早期表现出不同程度的rPR，并且随着产蛋季节的推进，rPR反应的发生率和严重程度会增加。此外，PRL和LH水平并未反映出对光周期变化有反应和无反应组之间产蛋量的差异。
