EFFECT OF EXOGENOUS GONADOTROPINS ON ESTRUS, THE LH SURGE AND THE TIMING AND RATE OF OVULATION IN RED DEER (CERVUS-ELAPHUS)

Red deer hinds (n = 38) were treated in the breeding season with five different gonadotrophin regimens to investigate the temporal relations hip between oestrus, ovulation and the LH surge. All hinds were treate d 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 dev ice 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 devi ce 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 crayon-harnessed stags to determine the time of oestrus onset. Blood samples were collected every 2 days for 26 days after CID R device removal to determine concentrations of plasma progesterone an d 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 af ter oestrus onset and was repeated twice at intervals of 12 h. Final o vulation rate was determined on day 7 after CIDR device removal. All h inds received 500 mu g cloprostenol i.m. on day 13. A total of 30 and 34 hinds exhibited oestrus and ovulation, respectively. Exogenous gona dotrophin 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 versu s 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 wit h 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 less than or equal to 12 h, whereas PMSG or PM SG and FSH induced ovulation over a period > 24 h. Treatment with exog enous,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 co ncentrations. Two hinds showed premature luteal regression. The admini stration of PGF(2 alpha) 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 admi nistration.