Induction of parturition in sheep using oestradiol benzoate

Abstract

The efficacy of oestradiol benzoate (ODB) in inducing parturition in Dorset Horn x Merino ewes was examined in two trials conducted at the Agricultural Research Station, Condobolin during the autumn and spring of 1974. In the first trial ewes were given either 10, 20 or 40 mg of ODB i.m. as a single dose between days 140 and 144 of gestation. In the three days following treatment 50 per cent of untreated ewes lambed. Of the treated ewes, 14.7 per cent lambed on the first day after treatment, 79.4 per cent lambed on the second day after treatment and 5.9 per cent lambed on the third day after treatment. Abortion was induced in 40 to 70 per cent of ewes inadvertently treated on days 126 to 130 of gestation, with all lambs born dead or dying. In a second trial ODB was effective in inducing parturition at doses as low as 7.5 mg. For ewes treated at 141 days of gestation optimal synchrony of parturition, between 35 and 50 hours after treatment, was obtained with doses of 20 and 30 mg ODB. Lamb losses (19 to 23 per cent) in treated ewes were similar to those for untreated ewes. ODB was superior to either a short or long acting corticoid (Dexamethasone) in synchronizing and inducing parturition in ewes treated at 141 days of gestation. Lambs born prematurely grew at least as well as lambs born at the normal time.