Red deer hinds (n = 38) were treated in the breeding season with five different gonadotrophin regimens to investigate the temporal relationship between oestrus, ovulation and the LH surge. All hinds were treated with progesterone-impregnated controlled internal drug release (CIDR) devices to synchronize oestrus. The five treatments were as follows: treatment 1, controls; treatments 2, 3 and 4, 1200 iu pregnant mares' serum gonadotrophin (PMSG) was administered i.m. 72 h before CIDR device withdrawal (treatments 3 and 4 were also injected i.v. with 0.4 mg synthetic GnRH 12 or 18 h after CIDR device withdrawal, respectively); treatment 5, 200 iu PMSG was administered i.m. 72 h before CIDR device withdrawal and 0.5 iu FSH was administered in eight equal doses at intervals of 12 h starting from the time of PMSG injection. The hinds were run with crayonharnessed stags to determine the time of oestrus onset. Blood samples were collected every 2 days for 26 days after CIDR device removal to determine concentrations of plasma progesterone and every 2 h for 72 h after CIDR device removal to determine plasma LH profiles. Laparoscopy for ovary examination was performed 6 or 12 h after oestrus onset and was repeated twice at intervals of 12 h. Final ovulation rate was determined on day 7 after CIDR device removal. All hinds received 500 μg cloprostenol i.m. on day 13. A total of 30 and 34 hinds exhibited oestrus and ovulation, respectively. Exogenous gonadotrophin administration advanced the onset of oestrus (21.1 ± 1.9 h versus 43.6 ± 2.6 h, P< 0.001) and ovulation (41.8 ± 3.1 h versus 71.3 ± 5.8 h, P < 0.001) and reduced the interval between the two events (19.1 ± 1.8 h versus 33.0 ± 0.0 h, P < 0.01). Treatment with CIDR devices alone resulted in one (n = 6) or two (n = 1) ovulation points. Exogenous gonadotrophins induced multiple ovulation points in most hinds. GnRH administration reduced the period over which multiple ovulations occurred to ≤ 12 h, whereas PMSG or PMSG and FSH induced ovulation over a period > 24 h. Treatment with exogenous gonadotrophins advanced the mean time to peak LH (17.1 ± 1.7 h versus 48.0 ± 3.1 h, P < 0.01) but had no effect on mean peak LH concentrations. Two hinds showed premature luteal regression. The administration of PGF_2α was effective in terminating luteal activity of multiple corpora lutea: progesterone concentration declined from 8.8 ± 1.4 to 0.6 ± 0.1 ng ml⁻¹ within 2 days of prostaglandin administration.

The luteolytic effect of the prostaglandin F_2α analogue, cloprostenol, was investigated in red deer by monitoring concentrations of plasma progesterone, the induction of oestrus and ovulation, and fertility. Oestrus was synchronized in 48 adult hinds by intravaginal delivery of exogenous progesterone for 12 days and i.m. injection of 250 iu pregnant mares' serum gonadotrophin at progesterone withdrawal. A single i.m. dose of 500 μg cloprostenol was administered at day 4, 6, 8, 10, 12, 14 or 16 of the subsequent oestrous cycle (n = 6 hinds per treatment; day 0 = oestrus). Six other hinds were monitored by intensive collection of blood samples between day 16 and day 19 to define changes in plasma progesterone concentrations during spontaneous luteolysis. Samples of jugular blood, collected every second day throughout the study and every 6 h for 78 h from the time of administration of cloprostenol, were analysed for plasma concentrations of progesterone and LH. Oestrus was detected by continuous observation during the period of intensive collection of blood samples and all hinds were subjected to transrectal ultrasonography to assess pregnancy status. On the basis of changes in plasma progesterone concentrations, cloprostenol induced complete luteolysis in all hinds treated on days 8–16 and in five of six hinds treated on day 6. Oestrus, ovulation and conception occurred in 25 (69%), 28 (78%) and 25 (69%), respectively, of hinds treated on days 6–16 inclusive (n = 36). Luteolysis was incomplete in all hinds treated on day 4, and none of the animals exhibited oestrus or ovulated; luteolysis was incomplete for one hind treated on day 6. Short luteal cycles (< 12 days duration) occurred in six hinds following cloprostenol treatment, but this occurred only in hinds treated on day 6 (n = 3), day 8 (n = 1) or day 10 (n = 2). The mean intervals from injection of cloprostenol to onset of oestrus and peak preovulatory LH surge values were significantly shorter for hinds treated on day 6 or day 8 (∼50 h and 52 h for oestrus and LH surges, respectively) than for those treated on days 10–16 inclusive (60 h and 65 h, respectively) (P < 0.05). It is concluded that on day 4 of the cycle, the cervine corpus luteum is refractory to a single injection of the prostaglandin analogue, whereas on day 6 the corpus luteum is responsive in most animals, and that whereas corpora lutea at days 8–10 are responsive in all animals, a high incidence of subsequent premature luteal regression may occur. Fertility to cloprostenol-induced oestrus and ovulation following natural mating was high, especially for hinds treated on days 12, 14 and 16 of the oestrous cycle (i.e., >80% conception rate).

The effects of administration of exogenous melatonin to pregnant red deer hinds on prolactin secretion, lactogenesis and reproductive seasonality were studied. Mature hinds (n = 23) were allocated to one of four treatments. Hinds in treatment 1 (n = 6) each received two subcutaneous melatonin implants (Regulin) at monthly intervals starting on 2 October, about 80 days before expected parturition. Hinds in treatment 2 (n = 6) received similar treatment starting on 2 November, about 40 days before calving, whereas hinds in treatment 3 (n = 5) received treatment starting on the actual day of calving (about 10 December). Final implants were delivered on 1 February, with overall treatment durations of 150, 120 and 90 days for treatments 1–3, respectively. Hinds in treatment 4 (n = 6) served as controls and received no melatonin treatment. Blood samples were taken twice a week from September to May, and plasma was analysed for progesterone and prolactin. Mammary development was assessed by palpation score (0–5) twice a week from October to April inclusive, and liveweights were recorded at least every two weeks throughout the trial. Calving occurred between 28 November and 24 December, with no significant differences among treatments (P > 0.10). Hinds in treatment 1 exhibited significant retardation of mammary gland development and liveweight gain leading up to parturition (P < 0.01). Furthermore, sex-adjusted calf birth weights were on average 3 kg lighter for treatment 1 (P < 0.05), with all calves either removed for bottle-rearing or having died within a few hours of birth. Failure of lactogenesis in treatment 1 was characterized by the presence of underdeveloped, hard mammary tissue devoid of expressible milk. Hinds in treatments 2–4 all exhibited full lactation and successfully reared their calves, and there were no significant differences in calf weaning weight and growth rates. Likewise, there were no significant differences in mean liveweight or lactation score profiles. Mean plasma prolactin concentrations varied significantly between treatments (P < 0.05), and control hinds exhibited a marked seasonal pattern of secretion which reached a peak at calving. However, hinds in treatments 1 and 2 failed to show any discernible seasonal increase in mean plasma prolactin concentrations, whereas there was a marked increase in mean prolactin concentrations in hinds in treatment 3 up to parturition, but concentrations decreased rapidly thereafter relative to those of control hinds. Melatonin treatment significantly advanced the date of first oestrus and decreased the postpartum–oestrus interval (P < 0.05). It was concluded that initiation of melatonin implant treatment about 80 days before parturition compromises mammary and fetal development in red deer hinds. However, the role of prolactin was not demonstrated conclusively.

In Expt 1, 59 mature fallow deer does were allocated to six treatments (n = 9–10 per treatment). Does assigned to treatments 1, 2 and 3 each received an i.m. injection of 500 μg cloprostenol on day 13 of a luteal cycle. Does in treatments 2 and 3 received 50 or 100 iu pregnant mares' serum gonadotrophin (PMSG), respectively, at the time of prostaglandin administration. Does assigned to treatments 4, 5 and 6 each received single intravaginal controlled internal drug release (CIDR) devices for 14 days. Does in treatments 5 and 6 received 50 or 100 iu PMSG, respectively, at the time of CIDR device withdrawal. Incidence of oestrus was higher following treatment with CIDR devices than with prostaglandin (29 of 30 versus 12 of 29, P < 0.001). PMSG induced earlier onset of oestrus (34.6 ± 0.9 h versus 44.7 ± 2.4 h, P < 0.01) and reduced the range in the time to onset of oestrus (from 22 to 8 h for prostaglandin-treated does and from 36 to 14 h for progesterone-treated does). The number of LH surges was higher following treatment with CIDR devices than with prostaglandin (10 of 12 versus 3 of 12, P < 0.01). The overall mean peak LH concentration and time to LH peak were 30.2 ± 3.4 ng ml⁻¹ and 45.2 ± 2.2 h after prostaglandin administration or CIDR device withdrawal. The overall median time of ovulation was 26 h after the onset of oestrus. The administration of 100 iu PMSG stimulated the incidence of luteinized follicles and twin corpora lutea. In Expt 2, 105 does were allocated to four treatments (n = 26–27 per treatment): prostaglandin; prostaglandin with 50 iu PMSG; CIDR devices; or CIDR devices with 50 iu PMSG. The does were inseminated cervically with 200 × 10⁶ frozen–thawed spermatozoa 12 h before the median time of ovulation as calculated for each treatment in Expt 1. The proportion of pregnant does was higher following treatment with CIDR devices than with prostaglandin (38 of 52 versus 28 of 53, P < 0.05). PMSG was beneficial only for does treated with prostaglandin. In Expt 3, 93 does were treated with CIDR devices for 14 days and inseminated cervically with 50 × 10⁶, 25 × 10⁶ or 12.5 × 10⁶ fresh spermatozoa at 12 h before the median time of ovulation. The concentration of spermatozoa had no effect on conception rate. The overall pregnancy rate was 76.3%.

Summary. The timing of ovulation relative to the onset of oestrus and the preovulatory surge in luteinizing hormone (LH) was studied in red deer following treatments to synchronize oestrus and induce either a monovulatory or superovulatory response. Mature hinds (n = 36) were allocated randomly to two mating groups (n = 16 + 20), with respective treatments staggered by 4 weeks during the 1990 rut (March–April). Each hind was treated with an intravaginal controlled internal drug releasing (CIDR)-type S device for 14 days. Treatments to induce a monovulatory response included CIDR device alone (treatment A; n = 4 + 8) and additional injection of 200 iu pregnant mares' serum gonadotrophin (PMSG) at device removal (treatment B; n = 4 + 4). Treatments to induce a superovulatory response included injections of 200 iu PMSG and 0·5 units ovine follicle-stimulating hormone (FSH) at about time of removal of CIDR devices (treatment C; n = 4 + 4) and further treatment with gonadotrophin-releasing hormone (GnRH) analogue 18 h after removal of CIDR devices (treatment D; n = 4 + 4). The hinds were run with crayon-harnessed stags from insertion of CIDR devices (12 March or 9 April) and blood samples were taken every second day to determine plasma progesterone. Further blood samples were collected for determination of plasma LH and progesterone via indwelling jugular cannulae every 2 h for 72 h from removal of CIDR devices. Hinds were allocated randomly to an initial ovarian examination by laparoscopy at either 16 or 20 h (A and B), or 12 or 16 h (C and D) after the onset of oestrus, with laparoscopy repeated at intervals of 8 h until either ovulation was recorded (A and B), or for four successive occasions (C and D). All hinds received cloprostenol injections 15 days after device removal.

A total of 28 hinds (78%) exhibited oestrus and a preovulatory LH surge, with mean (± sem) times to onset of oestrus of 44·6 ± 1·0 h (A; n = 7), 37·4 ± 2·0 h (B; n = 7), 16·3 ± 1·7 h (C; n = 6) or 14·0 ± 1·7 h (D; n = 8). Failure to exhibit oestrus or LH surge was most prevalent among hinds in treatment A early in the rut. For all treatments, the onset of oestrus occurred between 8 h before and 8 h after the LH peak and the mean (± sem) interval from onset of oestrus to (first) ovulation was 24·7 ± 1·0 h, 20·6 ± 1·0 h, 20·0 ± 2·9 h and 22·0 ± 3·2 h for treatments A–D, respectively. Superovulation was characterized by nonsynchronous ovulations, with no apparent differences between treatments C and D. Initial ovarian examination showed that 4·5% of total (day 15) ovulations had occurred 12–16 h after oestrus, increasing progressively to 80·7% by 36–40 h, indicating poor ovulation synchrony. The overall mean ovulation rate was 8·8 ± 1·1. Concentrations of progesterone during the luteal phase were correlated with ovulation rate. Administration of cloprostenol 15 days after removal of CIDR devices promoted luteal regression in all hinds, but return to oestrus occurred over seven days and two superovulated hinds retained multiple embryos to term despite treatment.

Keywords: red deer; oestrus; ovulation; luteinizing hormone; progesterone