Nutritional effects on puberty were studied in Soay rams. Testicular growth is initiated at birth in April and testes reach maximum size in October. Groups of eight lambs were fed for 18 weeks, starting in August, a ration that restricted growth (Group R), the same diet ad libitum (Group F), or a restricted diet for 8 weeks followed by ad libitum feeding (Group R/F). Seasonal increases of plasma FSH, testis size, sexual skin flush and plasma testosterone occurred with similar timing but reduced magnitude in Group R compared with Group F lambs. Testis size and sexual skin flush peaked in all groups at 11 weeks (30 October); the testes of Group F animals were larger before the peak, but similar in size thereafter, compared with testes from Group R/F, and larger throughout the experimental period than testes from Group R. Plasma testosterone was higher in Group F than in Group R lambs from 7 to 17 weeks, but in Group R/F was similar to Group R before 10 weeks (23 October) and similar to Group F thereafter. Testis size, plasma testosterone, plasma insulin-like growth factor I (IGF-I) and liveweight were positively correlated. Ad libitum feeding in August–September (Group F) stimulated increased plasma FSH and LH above values for Group R, but ad libitum feeding initiated in October did not affect gonadotrophin concentrations (Group R/F). Therefore, the effects of improved nutrition on the hypothalamo–pituitary axis, which may have been mediated by circulating IGF-I, were season- or age-dependent, and those on the testes included direct stimulation, independent of changes in gonadotrophin concentrations. Nutrition modified the intensity, but not the timing, of peak pubertal reproductive activation.

Male red deer calves, whose mothers had been kept for the last 14 weeks of gestation in long days (18 h light:6 h dark) (group L, n = 7) or short days (6 h light:18 h dark) (group S, n = 5), were kept in constant intermediate daylength (12 h light:12 h dark) from birth to 75 weeks of age. Both groups showed the same live-weight gain. Mean plasma LH concentrations were higher in group L than in group S from birth to 20 weeks of age (averaging 1.55 versus 0.48 ng ml⁻¹, P< 0.001), from 21 to 45 weeks (1.65 versus 1.32 ng ml⁻¹, P < 0.05) and from 46 to 50 weeks (1.84 versus 1.27 ng ml⁻¹, P < 0.001); thereafter, there was no significant difference between the groups (1.81 ng ml⁻¹). Mean concentration of plasma testosterone was relatively low from birth to 30 weeks (averaging 0.38 and 0.27 ng ml⁻¹ (P<0.05) in groups L and S, respectively), but thereafter increased to a maximum which was greater (2.78 versus 1.46 ng ml⁻¹, P < 0.01), and occurred earlier (47 versus 68 weeks of age, P < 0.001) and at lower body weight (82 versus 96 kg, P < 0.01) in group L compared with group S. Growth of antlers started in both groups at 25 weeks, but they hardened earlier in group L than in group S (42 versus 47 weeks of age, P< 0.05). These results provide evidence that in male red deer postnatal photoperiodic change is not required to trigger puberty, that prenatal photoperiodic history influences postnatal reproductive development and that the timing of reproductive maturation in deer raised on 12 h light:12 h dark is advanced by long days experienced prenatally.

Summary. Concentrations of progesterone in peripheral plasma of red deer hinds were basal ( < 1 ng/ml) during lactation/seasonal anoestrus, but increased abruptly at the onset of the breeding season. Lactating hinds (N = 19) started ovarian cycles 10 days later (P<0·01) and conceived 16 days later (P< 0·001) than did 13 weaned hinds. There was no evidence, from plasma progesterone values, of silent oestrus at the start of the season. Progestagen/PMSG treatment induced early ovulations in 8 anoestrous hinds but fertility was low, only 2 conceiving and giving birth. Pregnant hinds (N = 42) had high plasma concentrations of progesterone (mean 3–5 ng/ml) which declined just before parturition.

Summary. Lactating (N = 12) and non-lactating (N = 6) red deer hinds and one stag at pasture were given concentrates (500 g/head) containing melatonin (5 mg/head) daily at 16:00 h from 18 June to 16 October. The stag shed the antler velvet and started rutting 5 weeks ahead of untreated stags, and hinds had their first oestrus and ovulation of the breeding season in mid-September, 5 weeks in advance of control lactating (N = 9) and non-lactating (N = 5) hinds. Treated hinds were allowed to mate with the treated stag and control hinds ran in an adjacent paddock with an untreated stag. All hinds became pregnant during the study with all but 2 melatonin-fed hinds (1 lactating, 1 non-lactating) and 1 control hind (lactating) conceiving at the first oestrus.

Melatonin-treated hinds lost slightly more live weight than did controls from June to November, but their suckled calves grew throughout at a rate similar to those of control hinds.

Summary. From 17 February 1987 (Day 1) to 5 June 1988 (Day 475), 6 red deer hinds which had been in natural daylength (NL/M) and 6 hinds which had been in continuous artificial light for the previous month (CL/M) were each given melatonin (5 mg in feed) daily at 15:00 h. Six controls (C) received unsupplemented feed. From Day 1 all hinds were in natural daylight and ovarian cyclicity was assessed from plasma progesterone concentrations. Group C first went into anoestrus on 15 March 1987 (Day 27 ± 9·2 (s.e.m)), recommenced cyclicity on 23 October (Day 249 ± 2·3) and went into anoestrus again on 2 April 1988 (Day 411 ± 8·7). Group CL/M first went into anoestrus 31 days earlier (P < 0·05) on 12 February (Day –4 ± 7·8), before the start of melatonin treatment; 4 hinds then recommenced ovarian cycles 132 days earlier (P < 0·001) on 13 June (Day 117 ± 5·8) and continued to cycle for a longer period than did controls. Group NL/M hinds were cyclic at the start of melatonin feeding and continued to cycle for 1 year or more (N = 6). Plasma prolactin concentrations remained suppressed (< 20 ng/ml) for the duration of melatonin-feeding (Groups CL/M and NL/M) whereas control values (Group C) were elevated (20–120 ng/ml) between April and August (P < 0·05).

The ovarian response by hinds to melatonin therefore depends on initial reproductive status and recent photoperiodic history, and continued administration to cyclic hinds stimulates prolonged ovarian cyclicity irrespective of the time of year.

Keywords: red deer; melatonin; progesterone; ovarian cyclicity; out-of-season breeding; prolactin

Summary. Plasma prolactin concentrations were higher (P < 0·001) in newborn red deer calves whose mothers had been maintained for the last 14 weeks of gestation in long days (18 h light) (group L, n = 9) than in those whose mothers had been kept over the same period in short days (6 h light) (group S, n = 5). After transfer of all hinds and suckled calves on the day of birth to constant intermediate daylength (12 h light), prolactin concentrations decreased exponentially (P < 0·001) in group L calves, but not in group S, during the first 21 days. Thereafter, prolactin fell to a nadir in group L calves and rose to peak values in group S calves at 8–12 weeks post partum (P = 0·003), before converging again by 14 weeks. The pattern of prolactin secretion over the first 14 weeks of life was therefore significantly affected by prenatal photoperiod.

Plasma prolactin concentrations in the adult hinds were higher (P < 0·001) in group L than group S at 4–10 weeks before parturition; they were similarly high around parturition and fell thereafter to baseline values after 7 weeks.

These results provide evidence that deer fetuses respond to photoperiodic information, thereby acquiring a photoperiodic history in utero that influences postnatal responses to photoperiod.

Keywords: prolactin; gestation; photoperiod; deer

Red deer (Cervus elaphus) exhibit highly seasonal rhythms in physiology and behaviour. The influence of photoperiod on the timing of these changes begins in utero where the fetus receives photoperiodic information via the diurnal pattern of maternal melatonin secretion. The potential sensitivity of deer fetuses to melatonin was ascertained by mapping specific receptors and characterizing them using 2-[¹²⁵I]iodomelatonin and quantitative autoradiography in vitro. Specific binding occurred from day 31 of gestation onwards (term = 233 days) over the spinal nerves and respiratory system. At later stages of gestation binding occurred over the brain, particularly the brainstem, the pituitary gland, thyroid gland, gastrointestinal tract including the pancreas, metanephros, cochlea of the ear, spinal cord, and spinal and cranial nerves. Binding was abolished in the presence of 10⁻⁷ mol melatonin l⁻¹ and diminished in the presence of 10⁻⁴ mol GTPγS l⁻¹ (guanosine-5-0-(3-thiotriphosphate)), confirming that binding represented functional G-protein-coupled melatonin receptors. Characterization studies, carried out on fetal lung, revealed that binding was time-dependent, reaching equilibrium at about 3 h at room temperature (22°C), and saturable with a dissociation constant (K _d) of 104 pmol l⁻¹. This study demonstrates the presence of G-protein-coupled melatonin receptors over a wide range of tissues in red deer fetuses from early in gestation, indicating that in addition to its role in the communication of photoperiodic information to the fetus in this species, melatonin may be involved in fetal growth and development.

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 × 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.

An experiment was carried out to determine the pattern of follicular expression of mRNAs for aromatase, IGF-I receptor (IGF-IR), IGF-binding protein (IGFBP)-2, -4 and -5, leptin and the long form of the leptin receptor (Ob-Rb) in ten ewes infused with human recombinant leptin (n = 5; 1 μg/h) or saline (n = 5) for 72 h in the luteal phase of the oestrous cycle. At the end of infusion a follicular phase was induced with a luteolytic dose of a prostaglandin F2α analogue and the ovaries were collected 32 h later. One ovary from each ewe was serially sectioned at 10 μm using a cryostat at −20 °C. All follicles >1 mm in diameter were counted and probed with specific oligoprobes for aromatase, IGF-IR and IGFBP-2, -4 and -5 and specific riboprobes for leptin and Ob-Rb. Leptin mRNA was detected in theca and granulosa cells and Ob-Rb mRNA was detected only in granulosa cells, of some, but not all antral follicles. Leptin doubled the number of follicles with a diameter ≥3.5 mm (1.0 ± 0.36 (s.e.m.) vs 2.4 ± 0.24; control vs leptin; P < 0.02) but had no effect on the number of ≥1 < 3.5 mm follicles. Leptin had no effect on the number of follicles expressing aromatase mRNA but it decreased significantly the number of follicles expressing mRNA for IGF-IR (10.7 ± 0.79 vs 7.4 ± 0.81; control vs leptin; P < 0.05), IGFBP-2 (10.0 ± 0.82 vs 5.2 ± 0.87; control vs leptin; P < 0.05) and IGFBP-5 (5.2 ± 1.60 vs 1.2 ± 0.30; control vs leptin; P < 0.05). Leptin increased the diameter of IGFBP-2 mRNA-positive follicles (1.5 ± 0.15 vs 2.2 ± 0.31 mm; control vs leptin; P < 0.05) and increased follicular mRNA expression for IGFBP-2 (0.30 ± 0.021 vs 0.39 ± 0.027 arbitrary units; control vs leptin; P < 0.05) and IGFBP-5 (0.46 ± 0.019 vs 0.25 ± 0.053 arbitary units; control vs leptin; P < 0.05). The mRNA for IGFBP-4 was detected in the theca of only two follicles from the control group. Leptin increased the number of follicles expressing Ob-Rb mRNA (0.25 ± 0.25 vs 1.40 ± 1.17; control vs leptin; P < 0.05) but had no effect on the number expressing leptin mRNA. Leptin decreased plasma concentrations of oestradiol (P < 0.05) and increased concentrations of FSH (P < 0.001) and insulin (P < 0.001), with no effect on glucose concentrations. These data show that: (i) ovine granulosa cells express mRNA for Ob-Rb and leptin and (ii) leptin increased the number of follicles ≥3.5 mm. Furthermore, the data suggest that suppression of oestradiol production by leptin is not mediated by inhibition of aromatase gene expression. Finally, the data indicate that the action of leptin in ovarian follicles is mediated by the IGF system, because leptin increased mRNA expression of IGFBP-2 and -5. Leptin also decreased the number of follicles expressing IGF-IR and IGFBP-2 and -5. We suggest that these actions of leptin on the IGF system decrease the bioavailability of IGF-I, resulting in decreased oestradiol production.