Influence of placentally mediated fetal growth restriction on the onset ofpuberty in male and female lambs

The onset of puberty in prenatally growth-restricted versus normally grown lambs of both sexes, born in April and housed under natural photoperiod, wa s examined. Singleton pregnancies were established and adolescent ewes were offered a high or moderate nutrient intake throughout gestation. Placental mass was reduced (P < 0.001) in high compared with moderate intake dams an d resulted in the birth of growth-restricted and normal birth weight offspr ing, respectively. At birth, female lambs weighed 3.43 kg versus 5.03 kg (P < 0.001; n = 14 per group) and male lambs weighed 2.75 kg versus 5.18 kg ( P < 0.001; n = 7 per group) in growth-restricted and normal birth weight gr oups, respectively. Lambs suckled for 12 weeks and thereafter were fed ad l ibitum until week 43 of age. Growth-restricted lambs had lower preweaning l ive weight gains and this difference was more pronounced in male (P < 0.05) than in female lambs (P = 0.07). Thereafter, live weight remained lower (P < 0.05) in growth-restricted than in normally grown lambs of both sexes un til week 25 of age. In females, the time of onset of puberty was similar in the two groups. All females ovulated and there were no differences in the number of ovarian cycles recorded or in the incidence of aberrant ovarian f unction. In males, testosterone concentrations and testicular volume were l ower in growth-restricted compared with normally developed lambs from birth until weeks 28 and 35 of age, respectively (P < 0.05). The seasonal increa se in plasma testosterone concentrations occurred later in growth-restricte d than in normally developed lambs (P < 0.01) but the timing of maximum pea k concentrations was similar. Peak testosterone concentrations were lower ( P < 0.05) in growth-restricted than in normal male lambs.