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Summary. Sixteen Romney rams were utilized in a 2 × 2 factorial experiment designed to evaluate the effects on semen production of (i) contrasting lighting regimens, and (ii) pinealectomy or sham-operation.

Reversal of the annual photoperiodic cycle advanced the seasonal peak of fructose levels in semen by 4 months and also reduced percentages of unstained and morphologically normal spermatozoa. Pinealectomy abolished this advancement of peak fructose production and reduced overall concentrations and motility of spermatozoa. Moreover, towards the end of the study pinealectomized rams had higher ejaculate volumes than did sham-operated rams.

Testicular and accessory sex gland data obtained after the rams were killed showed a marked influence of the lighting regimen: high values from sham-operated rams in short daily photoperiods contrasted with depressed values from those in long daily photoperiods. Pinealectomized rams provided values midway between these extremes, a finding which suggested both anti- and pro-gonadotrophic roles for the pineal gland in rams.

Two experiments were conducted to test whether thyroid hormones are required for the cessation of the breeding season in female red deer. In Expt 1, 16 mature hinds were allocated early in the breeding season (May) to the following groups: thyroidectomized (THX), thyroidectomized and treated with subcutaneous thyroxine implants which increased plasma tri-iodothyronine to physiological concentrations (THX + T₄), or euthyroid controls. Plasma progesterone concentrations consistent with oestrous cyclicity were evident in all hinds during the breeding season (May–September) but after 23 September plasma progesterone concentrations became generally low (< 2.0 nmol l⁻¹) in control and THX + T₄ hinds. In contrast, thyroidectomized hinds not receiving thyroxine continued to exhibit circulating progesterone comparable with breeding season concentrations until the end of the experiment (late December). Nine hinds were ovariectomized or ovariectomized and thyroidectomized in May and treated with subcutaneous oestradiol-impregnated capsules, which were removed for periods of about 1 month during August, November and January, to test whether thyroid hormones are involved in the seasonal decline of LH secretion (Expt 2). In the presence of oestradiol, basal LH concentrations and episodic LH secretion were low during the non-breeding season (September–March) (P < 0.05). During this season, basal and GnRH-induced LH concentrations and LH pulse frequency remained similar for both groups except in the absence of oestradiol, when basal LH (3.1 ± 0.8 versus 1.3 ± 0.5 ng ml⁻¹, P < 0.05 and GnRH-induced LH (25.9 ± 3.6 versus 4.7 ± 0.4 ng ml⁻¹, P < 0.001) concentrations were higher in thyroidectomized hinds than in euthyroid hinds, respectively. Twenty-five hinds were ovariectomized and thyroidectomized during the breeding season and treated with subcutaneous thyroxine implants at different times to identify when thyroid hormones are required to be present to suppress LH concentrations during the non-breeding season in the absence of oestradiol. Thyroxine treatment at the beginning of or during the non-breeding season was effective in suppressing plasma LH concentration, but this action of thyroid hormones did not occur during the breeding season. These results indicate that, in red deer hinds thyroxine is required for termination of the breeding season and that thyroid gland secretions specifically block steroid-independent inhibition of reproductive activity during the non-breeding season. This inhibitory mechanism requires thyroid hormones to be present only from around the time of the end of the breeding season for their normal expression, and they remain responsive to thyroid hormones after this period.

Summary. Prepubertal red deer hinds were subjected to shortened daily photoperiod (8 h light per day, N = 3) or a daily (afternoon) melatonin injection (N = 4) for 83 days starting on 8 January, 2 weeks after the summer solstice. Compared with control hinds (N = 3) these treatments caused premature moulting of summer pelage, reduced serum prolactin concentrations to barely detectable levels about 34 days earlier than usual and advanced the date of mating. Calves were born earlier (P < 0·005) in the hinds exposed to a shortened photoperiod (12 November ± 1·7 days) and melatonin treatment (11 November ± 3·2 days) than in control hinds (13 December ± 7·9 days). Serum progesterone levels recorded before the first detected oestrus indicated that silent ovulations had occurred in many of the hinds (6 of 10) in this experiment. This study demonstrated the role of shortened daily photoperiod in red deer and indicated that the effects of reduced photoperiod observed were mediated by melatonin.

Summary. The effect of thyroid function on regulation of seasonal reproduction was investigated in three red deer stags thyroidectomized (THX) in summer (January 1988) in comparison with five thyroid-intact controls. Responses of luteinizing hormone (LH) and testosterone to a bolus injection of 10 μg gonadotrophin-releasing hormone (GnRH) were tested in July, October, December, February and April. Blood samples were collected at weekly intervals from December 1987 to June 1989 for measurement of testosterone, triiodothyronine (T3) and prolactin concentrations. Testis diameters were measured every 2 weeks. In October 1988 (spring), plasma LH concentrations of control stags were less responsive (P < 0·01) to stimulation by GnRH than those of THX stags; plasma testosterone concentrations and testis diameters were low and there was no increase in plasma testosterone concentrations after injection of GnRH in control stags during October or December (spring, early-summer). In contrast, THX stags maintained a testosterone response (P < 0·01) in these 2 months and did not exhibit any signs of a seasonal lack of reproductive activity at this time of year. Control stags cast antlers in spring whereas THX stags maintained hard antlers throughout the study. Concentrations of plasma T3 were not detected in THX stags from June 1988 onwards, but exhibited a seasonal pattern in control stags, with low concentrations during autumn and winter (April to July) and high concentrations in spring and summer (August to February). There was no effect of thyroidectomy on the seasonal pattern of prolactin secretion. These results show that thyroidectomy blocks the seasonal transition from the breeding to the nonbreeding season in red deer stags and support the hypothesis that thyroid hormones are required for this transition.

Keywords: thyroidectomy; seasonality; iuteinizing hormone; testosterone; prolactin; red deer

Summary. Entire bucks (N = 7) exhibited pronounced liveweight gains over spring and summer months (October–February), to reach a peak mean weight of 59·8 kg, and rapid liveweight losses over the rutting period (April–May) with a minimum mean liveweight of 54·2 kg. Mean neck girth and serum testosterone levels increased during late summer (January–March) and peaked at 387 mm and 12 ng/ml respectively immediately before the onset of the rut (April). Thereafter both measures declined during winter and spring months (June–December). Bucks castrated prepubertally (N = 11) exhibited similar but less pronounced changes in mean liveweight and neck girth, in the absence of any change in testosterone secretion. Peak mean testicular diameter of entire bucks (39 mm) occurred immediately before the rut and was followed by testicular regression over winter and spring months (June–November), such that the testes attained their minimum mean size of 18 mm diameter in early summer (November). Motile spermatozoa were absent from ejaculates collected in summer (November 1983, 1984; January 1984). However, ejaculates collected pre-rut (late March), immediately post-rut (June) and in early spring (September) contained successively increasing numbers of motile spermatozoa.

A further 14 polled, entire bucks were given orally 5 mg (N = 7; Group A) or 20 mg (N = 7; Group B) melatonin at 15:30h daily from 1 December 1983 to 14 January 1984 (45 days). Seven control bucks (Group C) received vehicle ration only. The measurements taken for bucks in Groups A and B were not significantly different (P > 0·1) on any sampling date and the data for these 2 groups were pooled. Mean serum testosterone concentrations and mean ejaculate volume were not significantly different between melatonin-treated and control bucks on any sampling date, although other measures exhibited significant differences (P < 0·05) at various treatment or post-treatment dates: melatonin-treated bucks showed a transiently greater increase in neck muscle development during and immediately after treatment, a slight retardation of liveweight gain between 45 and 75 days after treatment, an earlier peak in maximum mean testicular diameter and an earlier onset of sperm presence in ejaculates.

Summary. Concentrations of LH, progesterone, oestradiol-17β and androstenedione were measured in serum from blood samples collected from 6 fallow does every hour for 46 h during a spontaneous oestrus. Four does had similar serum hormone profiles, with a pronounced preovulatory LH surge (∼ 20 ng/ml) occurring within 4 h of the onset of oestrus, a small elevation (from 0·1 to 0·3 ng/ml) of progesterone at the onset of oestrus, a gradual but non-significant increase (up to 25 pg/ml) of oestradiol-17β and a marked 2-fold increase of serum androstenedione concentrations occurring immediately at the onset of oestrus. The remaining 2 does showed pronounced increases in serum progesterone concentrations at the onset of oestrus and a reduction in the initial LH surge. One of these does exhibited a second preovulatory LH surge within the sampling period.

Summary. A total of 18 fallow does, including pubertal, non-pregnant and pregnant adult does (6 per class), each received a single subcutaneous implant containing 18 mg melatonin on 4 occasions at 29–30-day intervals from 10 November 1986 (∼ 120-day treatment period). A further 18 contemporary does served as herd-mate controls. Two adult fallow bucks were treated the same and were run with the does until 16 March. Thereafter, 1 of 4 control bucks was run with the does until 1 June. Of the 6 pregnant does receiving implants within the last 40 days of their gestation, 4 failed to lactate after parturition in December 1986. The remaining 2 does successfully reared their fawns, as did the 6 contemporary controls. Mean (± s.e.m.) dates of first oestrus in 1987 were 27·6 February (±3·0 days) and 22·9 April (±0·8 days) for all treated and all control does respectively (P < 0·001). Pubertal does were generally later to exhibit first oestrus than were older does within their respective treatment groups. Return oestrus occurred only in 2 pubertal does (1 treated and 1 control) with remaining does conceiving to their first oestrus, as verified by plasma progesterone profiles. However, 5 (28%) of the treated does and 3 (17%) of the control does failed to maintain pregnancy and fawn in 1987. The mean (± s.e.m.) 1987 fawning date of the remaining does was 22·4 October (±2·7 days) for the treated group (N = 13) and 13·1 December (±0·8 days) for the control group (N = 15; P < 0·001). Mean (± s.e.m.) gestation length of treated does (238·9 ± 0·6 days) was significantly longer than that of control does (234·5 ± 0·4 days; P < 0·001). Of 13 fawns born to treated does, 4 (31%) died within 24 h of birth (mainly due to hypothermia) whereas all 15 fawns born to control does survived to weaning.

Melatonin-treated bucks exhibited a marked advancement of neck muscle hypertrophy during the treatment period and displayed normal rutting activity (e.g. vocalization) in response to early oestrus in the treated does.

Keywords: fallow deer; Dama dama; reproduction; melatonin; oestrus; progesterone