IMMUNIZATION OF EWES AGAINST ESTRADIOL-17-BETA IN AN ATTEMPT TO INCREASE THE YIELD OF VIABLE EMBRYOS WITH SUPEROVULATION

The effect of immunisation against oestradiol-17 beta (E-2) on fertili sation rates and of human chorionic gonadotrophin (hCG) in reducing th e proportion of unovulated follicles from superovulated ewes was exami ned. Forty South African Mutton Merino ewes were divided into four tre atments in a 2 x 2 factorial arrangement with four replications (block s). All ewes were synchronised with intravaginal progestagen sponges a nd superovulated with a combination of 700 IU of PMSG and 11 mg FSHp. Ewes were actively immunised against E-2 six weeks before superovulati on. hCG (1500 IU) was administered intravenously 6 h after the onset o f oestrus. Ewes were mated naturally. Recovered embryos were cultured for six days to assess their viability. At embryo recovery the mean an ti-E-2 antibody titre (bound 40% of tracer E-2) was 217 +/- 251. Immun isation had a positive effect (p < 0.05) on fertility, with 88.8 +/- 2 .8% of the recovered ova having been fertilised, as opposed to 79.3 +/ - 3.2% for control (no immunisation, no hCG) ewes. Immunisation had no significant effect on ovulation rate and did not improve the yield of viable embryos (immunised = 6.7 +/- 1.1; control = 7.5 +/- 1.3) per e we. Embryos from immunised ewes appeared to possess a reduced viabilit y. A significant (p < 0.05) interaction between immunisation and hCG t reatment was observed, with hCG increasing (p < 0.01) the percentage o f unovulated follicles in control, but not in immunised ewes. It is co ncluded that (a) immunisation of superovulated ewes against E-2 improv es the fertility of these ewes, probably by negating the effects of hi gh peri-ovulatory E-2 levels in these ewes, (b) immunisation against E -2 is not a feasible practice for increasing the yield of viable embry os of superovulated ewes and (c) hCG may have been administered too ea rly after the onset of oestrus, particularly in control ewes.