Summary. Adult female Bennett's wallabies were treated with reductions in daylength, melatonin implants or injections of melatonin 2 h before dusk in early or mid-seasonal reproductive quiescence. In early reproductive quiescence (5 weeks after the winter solstice) reproductive quiescence did not end in response to 3 or 5 h of reduced daylength or in response to injections (400 ng/kg) or implants (0·5 g in a Silastic rubber envelope) of melatonin. Reductions in daylength at this time of year did, however, result in an extension of the circadian pattern of melatonin secretion. In mid-reproductive quiescence (21 weeks after the winter solstice) treatment with a 5 h reduction in daylength, melatonin injections administered 2 h before dusk or melatonin implants did result in the termination of reproductive quiescence and reactivation of the quiescent corpus luteum within a period of 5 days. The results of these experiments indicate that, in early reproductive quiescence, the Bennett's wallaby is refractory to the influence of reduced daylength or melatonin, although capable of responding to such reduced days in terms of an increased duration of melatonin secretion. Bennett's wallabies therefore exhibit a refractoriness to short days similar to that of some seasonal eutherians although it remains to be established whether this refractory response is the cause of the transition to seasonal reproductive quiescence.

Summary. Antler and testicular cycles were studied in a group of free ranging axis deer stags kept out of doors in southern England. Within the herd, there was little evidence of a clear seasonal synchrony in the antler cycle. Detailed information obtained from 4 stags indicated that there was a fixed relationship between stage of the antler cycle and testis diameter; minimum testis diameter occurred 1–2 months after antler casting whereas maximum testis diameter occurred when stags were in hard antler. Changes in body weight, circumference of the neck and plasma testosterone concentrations largely paralleled those of testis diameter. Motile spermatozoa were collected at all stages of the testis cycle. Six animals in the early stages of antler growth were selected from the herd in May and 3 of these were implanted with 1 g melatonin in a Silastic rubber envelope. Each animal was captured on 3 subsequent occasions at monthly intervals. Melatonin was without effect on the rate of increase in size of the testis, circumference of the neck or growth and cleaning of the antlers although 1 of the treated animals failed to cast his antlers at the expected time 8 months after cleaning. We conclude from this study that there is little or no seasonal photoperiodic entrainment of the antler and testicular cycles of males in this population of axis deer.

Keywords: circannual cycles; antlers; aseasonal reproduction; axis deer

Summary. Adult female Bennett's wallabies (N = 6) were maintained in artificial winter solstitial daylengths commencing 3 weeks before the winter solstice for 16 or 42 weeks. Such treatment effectively prevented the normal establishment of seasonal reproductive quiescence with animals continuing to exhibit reproductive cycles beyond the time of the normal termination of the breeding season. Animals maintained in natural photoperiods or simulated natural changes in daylength after the winter solstice all entered reproductive quiescence by early February. In the Bennett's wallaby, therefore, the breeding season does not terminate as a result of refractoriness to short daylengths. Our results indicate that the relatively small increases in photoperiod shortly after the winter solstice provide the environmental signal responsible for initiating the onset of seasonal reproductive quiescence which normally occurs 5–8 weeks after the solstice. These results contrast with the effect of fixed artificial summer solstitial daylengths on the onset of the breeding season in which breeding begins spontaneously at the normal time of year as a result of long-day photorefractoriness.

Keywords: Bennett's wallaby; photoperiod; refractoriness; seasonality

Summary. Three groups of adult female wallabies were maintained out of doors under conditions of natural photoperiod and temperature from late December to mid-August. One group (M1; N = 6) received Silastic elastomer melatonin implants on 14 December, a second group (M2; N = 5) were given implants on 16 February and a third group (C; N = 7) were unimplanted controls. Group C animals had all ceased cycling by 15 March and the subsequent breeding season commenced on 5 July ± 6·9 days. Group M1 wallabies continued to cycle throughout the experimental period and did not exhibit ovarian quiescence. In Group M2, 2/5 animals continued to undergo repeated oestrous cycles and 3/5 ceased cycling between 14 December and 27 January and began again after the insertion of melatonin implants on 16 February. The prolactin response 30 min after s.c. administration of the dopamine antagonist domperidone was determined approximately every 4 weeks. In Group C, peak responses were high during the period of seasonal quiescence January–June; mean range 14·2–19·6 ng/ml) and fell significantly (P < 0·02) at the beginning of the breeding season in early July to 7·4 ± 3·1 ng/ml. In Group M1, prolactin levels remained low (2·8–8·2 ng/ml) throughout the course of the experiment while in Group M2, response to domperidone fell following the insertion of the implants and subsequently remained at levels similar to those in Group M1. Our data support the hypothesis that photoperiod-induced changes in the secretion of melatonin after the winter solstice drive this species into seasonal quiescence by influencing the dopaminergic control of prolactin secretion.

Keywords: Bennett's wallaby; seasonality; prolactin; melatonin

Summary. The oestrous cycles of fourteen red deer hinds (six yearling; eight more than 2 years old) were synchronized during the early breeding season by removal of a progesterone-containing intravaginal device and blood samples were taken at intervals of 3 h commencing 13 or 25 h later and continued for 54 h. The controlled internal drug release devices (CIDRs) were removed at 08:00 h (group 1; three yearlings and four adults) or 12 h later at 20:00 h (group 2; three yearlings and four adults). There was no significant effect of time of removal of CIDR on the interval to the onset of oestrus (group 1, 34·5 ± 4·05 h; group 2, 42·14 ± 7·8 h) on the time of peak concentration (group 1, 41·81 ± 5·69 h; group 2, 41·71 ± 7·81 h) or on duration of the luteinizing hormone (LH) surge (group 1, 15·00 ± 0·95 h; group 2, 14·57 ± 0·78 h). The six yearling animals exhibited oestrus and LH surge significantly later than the adults (55 ± 4·2 versus 32 ± 6·3 h for the LH surge for yearling and adult females, respectively). In a further experiment, 20 hinds were synchronized during the breeding season by removal of CIDR at two times of day 12 h apart and placed with a stag. Mating took place at a mean time of 42·1 ± 2·4 h and 37·0 ± 1·3 h later in the two groups. There was no significant effect of time of removal of CIDR upon time to onset of oestrus. These data indicate that the timing of ovulation and onset of sexual behaviour in this species is unlikely to be controlled by a circadian gate. The significant delay in onset of oestrus in young animals suggests that either social or developmental factors may play an important role in timing ovulation in red deer following the decline of progesterone.

Keywords: red deer; oestrus; luteinizing hormone surge; circadian rhythm

Two groups of adult female wallabies were maintained in photoperiod-controlled rooms from June 1987 until August 1988. Group SSH was held on summer solstice photoperiods throughout the experiment; group SN was subjected to weekly stepwise simulated natural changes in photoperiod. Plasma melatonin concentrations reflected photoperiod with high concentrations during the dark phase in both groups. Group SN wallabies commenced oestrous cyclicity on 21 July (±19 days, n = 6) entered reproductive quiescence on 14 February (± 10 days, n = 5) and recommenced cycling on 8 June (± 3 days, n = 4). Group SSH wallabies began cycling on 27 July (± 9 days, n = 7) at a time that was not significantly different from that of group SN. Three out of five of group SSH exhibited a spontaneous period of reproductive quiescence of between 59 and 70 days commencing between 3 December and 25 February. There was a highly significant difference between the transient plasma prolactin response to a dopamine antagonist during cycling and quiescent periods in both groups (P < 0.001) such that the response was increased during periods of quiescence. Our data support the hypothesis that prolactin is involved in the control of seasonal quiescence in the female Bennett's wallaby and demonstrate that spontaneous changes in reproductive state and prolactin can occur when animals are maintained on unchanging long photoperiods.

Summary. The breeding season of the non-lactating Bennett's wallaby terminates when animals enter the state of seasonal quiescence. To examine this transition, pouch young were removed from females at intervals which were 3, 4 or 8 weeks (6, 11 and 8 animals respectively) after the winter solstice. Within 48 days, 3, 1 and 1 females gave birth respectively, indicating that these animals were not in seasonal quiescence when pouch young were removed. Those animals which did not give birth were either in seasonal quiescence or had undergone a non-pregnant cycle. To differentiate between the 2 possibilities, techniques which would ensure the detection of pregnant and non-pregnant cycles were assessed in 8 females during the breeding season. As has been previously reported for the wallaby, changes in peripheral progesterone concentrations and the vaginal smear occurred during pregnant and non-pregnant reproductive cycles. In addition, mating was detected by marking the male with a mixture of coloured crayon and paraffin wax. It was concluded that reproductive cycles in female wallabies could be monitored by collecting blood samples 2 times each week for progesterone determination and daily examination of females for mating marks. These techniques were then used to study the onset of seasonal quiescence in 9 females. All animals continued to show reproductive cycles after the winter solstice and it was not until 10 weeks after the winter solstice that all animals were in seasonal quiescence. This represents an increase in the duration of the breeding season over that previously reported for this species.

Summary. The pattern of LH secretion and response to exogenous GnRH was determined on 5 occasions during seasonal anoestrus of the Père David's deer hind. LH pulse frequency was low (3·3 ± 0·6 pulses/18 h) in early anoestrus (February), increased significantly in mid-anoestrus (April; 8·4 ± 1·4 pulses/18 h) and thereafter declined slightly in late anoestrus (June; 6·3 ± 0·25 pulses/18 h). Mean LH concentrations also showed significant changes during anoestrus with higher levels in mid-anoestrus (April; 0·85 ± 0·12 ng/ml) when compared with other times (0·53 ± 0·05, 0·60 ± 0·10, 0·68 ± 0·06 and 0·71 ± 0·05 ng/ml for February, March, May and June, respectively). LH pulse amplitude showed no significant changes during the study. The LH response to intravenous injections of 2 μg GnRH was lowest in early anoestrus (February), increased significantly in mid-anoestrus (April) and remained high through late anoestrus. The response during the luteal phase was similar to that seen during late anoestrus. These results indicate that seasonal anoestrus in the Père David's deer hind is not a uniform state but is characterized by an early period of 'deep' anoestrus.

Keywords: LH; deer; GnRH; seasonal anoestrus; breeding season

Summary. Changes in the secretion of LH during the oestrous cycle were studied in 5 tame Père David's deer in which ovulation was synchronized with progesterone implants and prostaglandin injections. Plasma LH concentrations were measured in samples collected at 15-min intervals for a 36-h period, starting 16 h after the removal of the progesterone implants (follicular phase), and for a further 10-h period 10 days after the removal of the progesterone implants (luteal phase). In all animals, there was a preovulatory surge of LH and behavioural oestrus which occurred at a mean time of 59·6 h (± 3·25) and 69 h respectively following implant removal. LH pulse frequency was significantly higher during the follicular phase (0·59 ± 0·03 pulses/h) than the luteal phase (0·24 ± 0·2 pulses/h), thus confirming in deer findings from research on domesticated ruminants. There were no significant differences between the follicular and luteal phases in mean plasma LH concentrations (0·57 ± 0·09 and 0·74 ± 0·13 ng/ml) or mean pulse amplitude (0·99 ± 0·14 and 1·05 ± 0·21 ng/ml) for the follicular and luteal phase respectively. The long interval from the removal of progesterone to the onset of the LH surge and the absence of a significant difference in mean LH concentration or pulse amplitude in the follicular and luteal phases resemble published data for cattle but differ from sheep in which there is a short interval from luteal regression to the onset of the surge and a marked increase in LH pulse amplitude during the luteal phase.

Keywords: deer; LH; oestrous cycle; pulsatile secretion

Summary. Reproductive cycles were studied in a group of tame Père David's deer hinds. The non-pregnant hind is seasonally polyoestrous and, in animals studied over 2 years, the breeding season began in early August (2 August ± 3·3 days; s.e.m., N = 9) and ended in mid-December (18 December ± 5·7 days; N = 8) and early January (6 January ± 3·2 days; N = 11) in consecutive years. During the anoestrous period, plasma progesterone concentrations were low (0·2 ± 0·01 ng/ml) or non-detectable. There was a small, transient increase in progesterone values before the onset of the first cycle of the breeding season. In daily samples taken during an oestrous cycle in which hinds were mated by a marked vasectomized stag, progesterone concentrations remained low (<0·5 ng/ml) for a period of about 6 days around the time of oestrus, showed a significant increase above oestrous levels by Day 4 (Day 0 = day of oestrus) and then continued to increase for 18 ± 2·8 days to reach mean maximum luteal levels of 3·5 ± 0·6 ng/ml. The plasma progesterone profiles from a number of animals indicated that marking of the hinds by the vasectomized stag did not occur at each ovulation during the breeding season and therefore an estimate of the cycle length could not be determined by this method. In the following year, detection of oestrus in 5 hinds was based on behavioural observations made in the absence of the stag. A total of 19 oestrous cycles with a mean length of 19·5 ± 0·6 days was observed. However, on other occasions, the length of the luteal phase, as assessed by plasma progesterone concentrations, showed considerable variation.

During the breeding season, experiments were conducted to investigate synchronization of oestrus with exogenous progestagens. Oestrus occurred 32–90 h after progestagen removal. The changes in plasma progesterone concentrations which followed oestrus were similar to those seen after natural oestrus.

Keywords: deer; oestrous cycles; progesterone; behaviour