THE EFFECT OF PRENATAL PHOTOPERIODIC HISTORY ON THE POSTNATAL ENDOCRINE STATUS OF FEMALE LAMBS

Postnatal photoperiodic experience plays a pivotal role in determining the timing of ovarian activity in female lambs. This study examines w hether a photoperiodic history gained while in utero is able to influe nce this timing. Pregnant Soay ewes were maintained in either long day s (n = 7, 18 h light: 6 h dark; group PLD) or short days (it = 12, 6 h light: 18 h dark; group PSD) from 25 days of gestation. At birth, fem ale lambs (ii = 8 per group) were transferred to long days for 10 week s, 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 o f birth and three times weekly for the duration of the study and the r esulting plasma assayed for progesterone and prolactin. Although both gestational photoperiods produced. at best, abbreviated periods of ova rian activity, lambs born to ewes which experienced long days during g estation (group PLD) exhibited elevated plasma progesterone concentrat ions significantly earlier (P < 0.05) than lambs born to ewes exposed to short days during gestation (group PSD) (mean +/- SEM, 193 +/- 17 v ersus 244 +/- 14 days for. PLD and PSD groups, respectively. Plasma pr olactin concentrations in newborn lambs born between late December and early April were not affected by the ambient photoperiod. but reflect ed the artificial daylength experienced by their mothers during gestat ion. Lambs born to ewes maintained under long days during gestation (g roup PLD) had significantly higher prolactin concentrations on the day of birth than lambs born to ewes maintained under short days during g estation (group PSD) (45 +/- 5.4 ng/ml versus 7 +/- 3.7 ng/ml respecti vely, 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 si gnificantly between treatment groups. These results suggest that the o vine foetus is sensitive to photoperiodic information prior to birth, and develops a photoperiodic history which, under the present experime ntal conditions, modulates the subsequent endocrine status of the neon atal lamb. (C) 1997 Elsevier Science B.V.