In female sheep, photoperiod regulates the timing of the transition to
adulthood. We tested the hypothesis that photoperiod very early in de
velopment influences the timing of the pubertal LH rise that initiates
sexual maturation. The first experiment was designed to determine the
influence of day length information perceived before birth by varying
prenatal photoperiod experience. Two groups that experienced either i
ncreasing or constant long days prenatally, and then a gradually decre
asing photoperiod postnatally, reached puberty at the same age (Prenat
al Increase, 20.4 +/- 0.5 wk vs. Prenatal Long Days [LD], 19.4 +/- 0.8
wk). Puberty in these groups was much earlier than in two control gro
ups exposed to the same photoperiods, but beginning at birth, for 13 w
k (Postnatal Increase, 29.6 +/- 1.0 wk; Postnatal LD, 26.2 +/- 1.3 wk)
. In the second experiment, the role of prenatal photoperiod in timing
sexual maturity was also examined through the use of treatments with
greater contrast. Lambs were exposed prenatally to either decreasing o
r increasing day lengths. Beginning at birth, both groups were exposed
to a decreasing photoperiod. Although only half of the lambs in each
group exhibited the pubertal LH rise, those that attained puberty did
so at the same age (Prenatal Decrease, 14.8 +/- 1.0 wk vs. Prenatal In
crease, 14.8 +/- 0.3 wk). We therefore conclude that day length cues e
xperienced postnatally predominantly time sexual maturation in the fem
ale lamb.