Koch J M, Moritz J S, Lay D C, Wilson M E
Division of Animal and Veterinary Science, Davis College of Agriculture, Forestry and Consumer Sciences, West Virginia University, Morgantown, WV, United States.
Anim Reprod Sci. 2007 Nov;102(1-2):14-23. doi: 10.1016/j.anireprosci.2006.09.023. Epub 2006 Sep 20.
Inducing hens to molt increases egg quality, egg production and extends the productive life of hens. It has been previously demonstrated that melengestrol acetate (MGA), an orally active progestin, decreased gonadotropic support for the ovary, which decreased the steroidogenic support for the oviduct and resulted in the cessation of lay. Estradiol produced by the theca cells of small follicles stimulates the production of the yolk proteins vitellogenin II and apolipoprotein II by the liver and supports the oviductal epithelial cells. The objective of the present experiment was to determine gene expression for yolk proteins and oviductal epithelial cell turn-over in response to a MGA-induced molt. Hy-Line W-36 laying hens were fed either 0 or 8mg MGA per day for 28 days in a balanced diet and then returned to a standard layer ration until day 36. Four birds per treatment on days 1, 8, 16, 28 and 36 were euthanized and the liver was removed and snap frozen in liquid nitrogen until RNA was extracted. Expression of vitellogenin II and apolipoprotein II genes was determined using real-time RT-PCR. A portion of the magnum was removed to determine proliferation and programmed cell death for secretory and ciliated luminal epithelium. Vitellogenin II and apolipoprotein II gene expression was reduced in hens fed 8mg MGA compared to those fed 0mg MGA. There was no effect of day on gene expression of either yolk protein. Cell proliferation was increased in the ciliated epithelial cells of the oviduct in hens receiving 8mg MGA compared to those receiving 0mg. However, programmed cell death of the ciliated epithelial cells was not different between controls and MGA treatment. Programmed cell death and proliferation increased in the secretory epithelial cells in hens receiving 8mg MGA compared to controls. Therefore, utilizing MGA as an alternative method to induce molt results in some, but not all, of the physiological changes previously described for hens molted by feed withdrawal. These findings lead us to suggest that some of the observed physiological changes resulting from feed withdrawal are required to increase egg quality and egg production following molt and other changes are not necessary, but are just a result of nutrient deprivation.
诱导母鸡换羽可提高蛋的品质、产蛋量并延长母鸡的生产寿命。先前已有研究表明，醋酸美仑孕酮（MGA）这种口服活性孕激素可减少对卵巢的促性腺激素支持，进而减少对输卵管的类固醇生成支持，导致产蛋停止。小卵泡的卵泡膜细胞产生的雌二醇会刺激肝脏产生卵黄蛋白卵黄生成素II和载脂蛋白II，并维持输卵管上皮细胞的功能。本实验的目的是确定在MGA诱导换羽的情况下，卵黄蛋白的基因表达以及输卵管上皮细胞的更新情况。海兰W-36蛋鸡在平衡日粮中每天分别饲喂0或8毫克MGA，持续28天，然后恢复至标准蛋鸡日粮直至第36天。在第1、8、16、28和36天，每组处理选取4只鸡进行安乐死，取出肝脏并迅速在液氮中冷冻，直至提取RNA。使用实时逆转录聚合酶链反应（RT-PCR）测定卵黄生成素II和载脂蛋白II基因的表达。取出一部分输卵管膨大部，以确定分泌性和纤毛性管腔上皮细胞的增殖和程序性细胞死亡情况。与饲喂0毫克MGA的母鸡相比，饲喂8毫克MGA的母鸡中卵黄生成素II和载脂蛋白II基因表达降低。日龄对两种卵黄蛋白的基因表达均无影响。与接受0毫克MGA的母鸡相比，接受8毫克MGA的母鸡输卵管纤毛上皮细胞的细胞增殖增加。然而，对照组和MGA处理组之间纤毛上皮细胞的程序性细胞死亡并无差异。与对照组相比，接受8毫克MGA的母鸡分泌性上皮细胞的程序性细胞死亡和增殖增加。因此，利用MGA作为诱导换羽的替代方法会导致一些但并非所有先前描述的因停喂饲料而换羽的母鸡出现的生理变化。这些发现使我们认为，停喂饲料后观察到的一些生理变化是换羽后提高蛋品质和产蛋量所必需的，而其他变化并非必要，只是营养缺乏的结果。
