Aw. Lishman et al., IMMUNIZATION OF EWES AGAINST ESTRADIOL-17-BETA IN AN ATTEMPT TO INCREASE THE YIELD OF VIABLE EMBRYOS WITH SUPEROVULATION, South African journal of animal science, 27(3-4), 1997, pp. 69-75
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.