R Ortavant

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The intensity of negative feedback of androgens on hypothalamo-hypophyseal activity was compared in two groups of castrated rams under 8.00 or 16.00 h of daily illumination respectively following a conditioning period. In experiment I, two groups of 15 rams under each light photoperiod were slaughtered at different times after a 200 mg testosterone(More)
The control of seasonal reproductive activity in sheep and goats in open sheds, needs extra-light (E) during the photosensitive phase (equivalent to long days, LD), followed by treatment with melatonin (equivalent to short days, SD). In autumn-born Ile-de-France or Lacaune ram lambs, 2 months of E followed by decreasing daylength for 90 days, advanced onset(More)
The influence of variations in the duration of light photoperiod on LH release has been studied in intact and castrated rams submitted to a 6 months "annual" light rhythm. Blood was collected once a month and the plasma LH levels were determined by radioimmunoassay. In intact rams, the LH level is decreased when the light photoperiod is increased, but as(More)
Using "skeleton" photoperiods with a primary photofraction of 3 hrs. 30 min. and secondary photofraction of 30 min. located at various intervals after the onset of darkness, the occurrence of a photoinducible phase in the androgenic function has been evidenced in the Ferret. This photo-inducible phase seems to be located around 12 hrs. after the onset of(More)
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