Sharp P J, Dunn I C, Cerolini S
AFRC Institute of Animal Physiology and Genetics Research, Edinburgh Research Station, Roslin, Midlothian, UK.
J Reprod Fertil. 1992 Jan;94(1):221-35. doi: 10.1530/jrf.0.0940221.
Egg-laying in hens exposed for more than 11 months to photostimulatory daylengths was intermittent and associated with a reduction in numbers of yellow-yolky ovarian follicles. Old laying hens (105 weeks) had lower concentrations of luteinizing hormone (LH) in the pituitary gland and plasma and reduced pituitary gland responsiveness to chicken LH-releasing-hormones (LHRH-I and II) in vivo when compared with young laying hens (28 weeks). Four weeks after transfer from 14 to 8 h light/day, egg production almost stopped in old, but not in young hens, although plasma LH concentrations decreased in all birds. After transfer from 14 to 20 h light/day, plasma LH increased in young, but not in old, hens, without a change in the rate of egg production. Reproductive function was enhanced in old hens returned to long days after induction of a moult and ovarian regression by reducing daylength and dietary restriction. Moulted hens had a greater rate of egg production, higher concentrations of plasma LH and a greater pituitary-gland responsiveness to LHRH-II in vivo than unmoulted control hens. After transfer from 14 to 8 h light/day, egg-laying decreased more rapidly in unmoulted than in moulted hens; transfer to 17 h light/day increased egg production in moulted, but not in unmoulted, birds. Induction of ovarian regression in old hens by dietary restriction alone also enhanced reproductive function after the dietary restriction was relaxed. Egg-laying was more persistent in hens brought into lay for a second year by transferring them from 3 to 11 h light/day than in hens transferred from 3 to 20 h light/day. Egg production was stimulated in hens maintained on 3 or 11 h light/day for 42 weeks, after transfer to 20 h light/day. Egg production ceased in hens maintained on 20 h light/day for 46 weeks, after transfer to 3 h light/day. These observations are consistent with the view that poor persistence of laying in hens less than 2 years old and exposed continuously to long days is caused, in part, by a reduction in hypothalamic-gonadotroph function. This reduction in neuroendocrine function may be due, in part, to the development of relative photorefractoriness.
暴露于光刺激日照长度超过11个月的母鸡产蛋是间歇性的，且与黄色卵黄卵巢卵泡数量减少有关。与年轻产蛋母鸡（28周龄）相比，老龄产蛋母鸡（105周龄）垂体和血浆中促黄体生成素（LH）浓度较低，且垂体在体内对鸡促黄体生成素释放激素（LHRH-I和II）的反应性降低。从14小时光照/天转变为8小时光照/天4周后，老龄母鸡的产蛋几乎停止，但年轻母鸡没有，尽管所有鸡的血浆LH浓度均下降。从14小时光照/天转变为20小时光照/天后，年轻母鸡的血浆LH升高，但老龄母鸡没有，产蛋率也没有变化。通过缩短日照长度和限制饮食诱导换羽和卵巢退化后，再恢复到长日照的老龄母鸡的生殖功能增强。与未换羽的对照母鸡相比，换羽母鸡的产蛋率更高，血浆LH浓度更高，垂体在体内对LHRH-II的反应性更强。从14小时光照/天转变为8小时光照/天后，未换羽母鸡的产蛋下降速度比换羽母鸡更快；转变为17小时光照/天后，换羽母鸡的产蛋增加，但未换羽母鸡没有。仅通过限制饮食诱导老龄母鸡卵巢退化，在放松饮食限制后也能增强生殖功能。将母鸡从3小时光照/天转变为11小时光照/天饲养至第二年，其产蛋比从3小时光照/天转变为20小时光照/天的母鸡更持续。在维持3或11小时光照/天42周后，将母鸡转变为20小时光照/天，产蛋受到刺激。在维持20小时光照/天46周后，将母鸡转变为3小时光照/天，产蛋停止。这些观察结果与以下观点一致，即不到2岁且持续暴露于长日照的母鸡产蛋持续性差部分是由于下丘脑-促性腺激素功能降低所致。这种神经内分泌功能的降低可能部分归因于相对不应性的发展。
