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Relationship between the onset of oestrus, the preovulatory surge in luteinizing hormone and ovulation following oestrous synchronization and superovulation of farmed red deer (Cervus elaphus)

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

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