FERTILITY IN MERINO EWES IN ARTIFICIAL INSEMINATION PROGRAMMES FOLLOWING SYNCHRONIZATION OF OVULATION USING CLOPROSTENOL, A PROSTAGLANDIN ANALOGUE I.J. FAIRNIE*+ and R.G. WALES* SUMMARY

Ten field and laboratory experiments were conducted in which Merino ewes were treated with one or two 125pg injections of Cloprostenol, an analogue of prostaglandin F2a (PG). All treatments commenced in the luteal phase of the oestrous cycle. Sixty-six percent of ewes were detected in behavioural oestrus within 64 hr of completion of treatments although 95 % of all treated ewes ovulated in apparent synchrony. The time of onset of behavioural oestrus was earlier in ewes treated with two injections of PG eight days apart compared to treatments with two injections of PG 11 or 14 days apart. Fertility, as assessed from the number of preimplantation embryos obtained by flushing oviducts and uteri of inseminated ewes, was lower in ewes treated with two injections of PG eight days apart when compared to unsynchronized control ewes. The results indicate that the timing between injections of PG is critical for ewe fertility and this may reflect the need for adequate progesterone priming of the reproductive tract to achieve normal fertilization rates in artificially inseminated ewes