Effect of restricted nutrition on timing of puberty in female Soay sheep

Ovariectomized, oestradiol-implanted Soay ewe lambs from 21 September (aged 21 weeks) had restricted (liveweight maintenance) (n = 4) or unrestricted food (n = 4); ovary-intact lambs had unrestricted food (n = 8). LH activation in ovariectomized lambs on restricted and unrestricted food and onset of ovulatory cycles in ovary-intact lambs all occurred on 7 December (SED 8.8 days) (32 weeks), but at different liveweights (24.2, 17.9 and 18.3 kg, respectively, SED 1.22). LH pulse frequency was similar in ovariectomized lambs on restricted and unrestricted food. From 29 August (aged 18 weeks), Soay ewe lambs in seasonally advanced decreased artificial daylength were given restricted food, unrestricted food, or food was restricted for 8 weeks and then unrestricted (n = 8 per group). Ovarian cycles started 3 weeks earlier than in lambs in natural photoperiod on similar dates for all three groups (14, 18 and 19 November, respectively, SED 5.5 days) (29 weeks), but at different liveweights (16.2, 20.7, and 18.4 kg, respectively, SED 0.87). From 1 August, Suffolk x Greyface ewe lambs (aged 16 weeks) had restricted food, unrestricted food, or food restricted for 8 weeks and then unrestricted (n = 8 per group). By 1 November (29 weeks), 0/8 lambs on restricted food (29.3 +/- 0.92 kg) but 8/8 lambs on unrestricted food and 5/8 lambs on 8 weeks of restricted food had ovulated (mean dates: 16 October +/- 2.5 days (27 weeks, 40.1 +/- 1.02 kg), and 1 November +/- 3.0 days (29 weeks, 35.5 +/- 1.23 kg), respectively. Thus, nutritional growth restriction during the 11 weeks preceding normal puberty delayed pubertal date in the improved breed but did not influence the timing of puberty in the unimproved Soay breed within the weight range studied.