Lambing and placental expulsion time after dexamethasone-induced parturition in Corriedale and Polwarth ewes.

To study breed differences in ewes induced to parturition with dexamethasone (DXM), 15 Corriedale and 16 Polwarth ewes were injected with 15 mg of DXM four days before the expected lambing date (Days 144 and 145, respectively) in Experiment 1. Interval from treatment to parturition was twice as long for the Polwarth than for the Corriedale breed (57.9 vs 28.8 hours, P </= 0.001). In Experiment 2, the effect of DXM on the interval from parturition to expulsion of the placenta and on biological parameters of the lambs (birth weight, ability to stand after birth and daily weight gain during the first week of life) was studied in 30 Corriedale ewes. On Day 144 of gestation, ewes were given 15 mg of DXM (n= 22) or 15 ml of saline (controls, n= 8). The DXM group lambed 33.8 +/- 2.7 hours after injection. Treatment caused an increase in the time of placental expulsion (4.3 vs 3.4 hours, P>/= 0.05) and on the percentage of ewes retaining the placenta beyond 6 hours (18% vs 0%, P>/= 0.05). Birth weight of lambs was lower in the induced group (3.9 vs 4.5 kg, P</= 0.03), but this did not affect the other parameters of the lambs studied.