Effect of exogenous gonadotrophins on oestrus, the LH surge and the timing and rate of ovulation in red deer (Cervus elaphus)
in ReproductionRed 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 PGF2α 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.
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