ESTROUS SYNCHRONIZATION IN EWES - THE EFFECT OF COMBINING A PROSTAGLANDIN ANALOG WITH A 5-DAY PROGESTAGEN TREATMENT

An experiment was designed to determine whether combining a single injection of 125 mug prostaglandin F2alpha analogue (PGF) with a 5-day progestagen pessary treatment (PPT) would obviate the problem with refractory animals that occurs when randomly cycling ewes are synchronized with PGF alone. The efficacy of the combined treatment, in comparison with single and double dose PGF regimes, was also assessed. A total of 210 ewes were used in this investigation conducted during the 1989 and 1990 breeding seasons. In both breeding seasons, 100% of the ewes treated with PGF combined with PPT were mated by fertile rams within a 3-day period, compared with 52.9% of ewes treated with a single injection PGF or 100% of ewes treated with two injections of PGF, 11-days apart. Returns to service for the three groups were 14.2%, 16.2% and 17.4%, respectively. There was no effect of treatment on lambing performance in 1989. However, in 1990 there were differences between groups in gestation length and birth weight, but these were attributable to enzootic abortion. The results demonstrate that PGF combined with PPT will produce levels of oestrous synchronization and fertility comparable with other methods.