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 unr estricted food (n = 4); ovary-intact lambs had unrestricted food (n = 8). LH activation in ovariectomized lambs on restricted and unrestrict ed food and onset of ovulatory cycles in ovary-intact lambs all occurr ed on 7 December (SED 8.8 days) (32 weeks), but at different liveweigh ts (24.2, 17.9 and 18.3 kg, respectively, SED 1.22). LH pulse frequenc y was similar in ovariectomized lambs on restricted and unrestricted f ood. From 29 August (aged 18 weeks), Soay ewe lambs in seasonally adva nced decreased artificial daylength were given restricted food, unrest ricted food, or food was restricted for 8 weeks and then unrestricted (n = 8 per group). Ovarian cycles started 3 weeks earlier than in lamb s in natural photoperiod on similar dates for all three groups (14, 18 and 19 November, respectively, SED 5.5 days) (29 weeks), but at diffe rent liveweights (16.2, 20.7, and 18.4 kg, respectively, SED 0.87). Fr om 1 August, Suffolk x Greyface ewe lambs (aged 16 weeks) had restrict ed food, unrestricted food, or food restricted for 8 weeks and then un restricted (n = 8 per group). By 1 November (29 weeks), 0/8 lambs on r estricted food (29.3 +/- 0.92 kg) but 8/8 lambs on unrestricted food a nd 5/8 lambs on 8 weeks of restricted food had ovulated (mean dates: 1 6 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, nutrition al growth restriction during the 11 weeks preceding normal puberty del ayed pubertal date in the improved breed but did not influence the tim ing of puberty in the unimproved Soay breed within the weight range st udied.