ESTRUS SYNCHRONIZATION IN EWES - THE EFFECT OF COMBINING A PROSTAGLANDIN ANALOG WITH A GNRH AGONIST (BUSERELIN)

An experiment was designed to determine whether an injection of 4 mu g of rite GnRH agonist buserelin (GnRH) followed, 5 days injection of 1 00 mu g of prostaglandin F2 alpha analogue (PGF), would give a level o f oestrus synchronization and fertility comparable with a standard dou ble dose PGF regime. A total of 200 Welsh Halfbred ewes were divided b y live weight into two treatment groups using a system of random strat ification during the 1994 breeding season. Ninety-one percent of the e wes treated with GnRH combined with PGF were mated by fertile rams wit hin a 3-day period compared with 94% of ewes treated with two injectio ns of PGF, 11-days apart. Returns to service for the two groups were 1 1 . 1% and 7 . 4%, respectively. There was no effect of treatment on l ambing performance, as a similar percentage of ewes in the GnRH plus P GF group (88 . 8%) and the double dose PGF group (92 . 5%) lambed to s ynchronized oestrus. Gestation length, litter size and birth weight we re similar for both groups. These results demonstrate that GnRH combin ed with PGF will produce levels of oestrus synchronization and fertili ty comparable with a double dose PGF regime.