Helliwell R J, Wallace J M, Aitken R P, Racey P A, Robinson J J
Rowett Research Institute, Aberdeen, UK.
Anim Reprod Sci. 1997 Jul;47(4):303-14. doi: 10.1016/s0378-4320(97)00018-3.
Postnatal photoperiodic experience plays a pivotal role in determining the timing of ovarian activity in female lambs. This study examines whether a photoperiodic history gained while in utero is able to influence this timing. Pregnant Soay ewes were maintained in either long days (n = 7, 18 h light: 6 h dark; group PLD) or short days (n = 12, 6 h light: 18 h dark; group PSD) from 25 days of gestation. At birth, female lambs (n = 8 per group) were transferred to long days for 10 weeks, and then placed under short days until the end of the experiment at 38 weeks of age. Blood samples were collected from lambs on the day of birth and three times weekly for the duration of the study and the resulting plasma assayed for progesterone and prolactin. Although both gestational photoperiods produced, at best, abbreviated periods of ovarian activity, lambs born to ewes which experienced long days during gestation (group PLD) exhibited elevated plasma progesterone concentrations significantly earlier (P < 0.05) than lambs born to ewes exposed to short days during gestation (group PSD) (mean +/- SEM, 193 +/- 17 versus 244 +/- 14 days for PLD and PSD groups, respectively. Plasma prolactin concentrations in newborn lambs born between late December and early April were not affected by the ambient photoperiod, but reflected the artificial daylength experienced by their mothers during gestation. Lambs born to ewes maintained under long days during gestation (group PLD) had significantly higher prolactin concentrations on the day of birth than lambs born to ewes maintained under short days during gestation (group PSD) (45 +/- 5.4 ng/ml versus 7 +/- 3.7 ng/ml respectively, P < 0.001). The mean birth weight, rate of live weight gain and live body weight of lambs at the end of the experiment did not vary significantly between treatment groups. These results suggest that the ovine foetus is sensitive to photoperiodic information prior to birth, and develops a photoperiodic history which, under the present experimental conditions, modulates the subsequent endocrine status of the neonatal lamb.
出生后的光周期经历在决定雌性羔羊卵巢活动的时间方面起着关键作用。本研究考察了在子宫内获得的光周期经历是否能够影响这一时间。从妊娠25天起，将怀孕的索艾羊分别饲养在长日照（n = 7，18小时光照：6小时黑暗；PLD组）或短日照（n = 12，6小时光照：18小时黑暗；PSD组）环境中。出生时，将雌性羔羊（每组n = 8）转移到长日照环境中饲养10周，然后置于短日照环境中直至38周龄实验结束。在出生当天以及研究期间每周三次采集羔羊血样，对所得血浆进行孕酮和催乳素检测。尽管两种妊娠期光周期条件下，羔羊的卵巢活动期充其量都有所缩短，但妊娠期经历长日照的母羊所生的羔羊（PLD组）血浆孕酮浓度显著升高的时间比妊娠期经历短日照的母羊所生的羔羊（PSD组）要早（P < 0.05）（PLD组和PSD组的平均值±标准误分别为193±17天和244±14天）。12月下旬至4月初出生的新生羔羊血浆催乳素浓度不受环境光周期的影响，而是反映了其母亲在妊娠期所经历的人工日照长度。妊娠期饲养在长日照环境中的母羊所生的羔羊（PLD组）出生当天的催乳素浓度显著高于妊娠期饲养在短日照环境中的母羊所生的羔羊（PSD组）（分别为45±5.4 ng/ml和7±3.7 ng/ml，P < 0.001）。实验结束时，各处理组羔羊的平均出生体重、体重增加率和活体体重没有显著差异。这些结果表明，绵羊胎儿在出生前对光周期信息敏感，并形成了一种光周期经历，在当前实验条件下，这种经历会调节新生羔羊随后的内分泌状态。
