Abstract
This study was conducted to investigate the effect of times of PMSG injection and ram introduc-tion on estrus incidence and lambing rate in ewes treated during the non-breeding season. During April to May, 85 Suffolk ewes were treated with an intravaginal sponge containing 60 mg medroxyprogesterone acetate for 9 days. Therefore, a factorial study (2×2) was designed for times of PMSG injection and ram introduction (The day of sponge removal: Day 0 and 2 days before sponge removal: Day-2); group I: 600 IU PMSG injection (Day 0) + ram introduction (Day 0), group II: 600 IU PMSG ineection (Day 0)+ ram introduction (Day-2), group III: 600 IU PMSG injection (Day-2) + ram introduction (Day 0) and group IV: 600 IU PMSG injection (Day-2)+ ram introduction (Day-2). Estrus was examined at 6 hr intervals after joining for 4 days. Ewes were injected a 100 μg LH-RH analogue at estrus detection, and after 9 hr mated by a hand service with one of four fertile rams. Semen characteristics of each ram at 57 hr after sponge removal examined. The results were as follows.
1) The rate of estrus incidence within 4 days after treatment were higher in groups where PMSG was injected at Day 0 than Day-2, regardless of the times of teaser rams introduction (100%, 95.2%, 90.0% and 85.0% for groups I, II, III and IV, respectively). One ewe in group IV exhibited silent estrus 24 hr before sponge removal.
2) The lambing rates were 75.0%, 60.0%, 66.7% and 87.5% for groups I, II, III and IV, respec-tively. Group IV showed a significantly higher lambing ratethan group II (P<0.05).
3) Semen characteristics and increased times of services did not affect lambing rates and prolifi-cacy in the 4 rams used.
These results suggested that the decrease of estrus incidence when PMSG was injected at 2 days before sponge removal involved an undeterminate or silent estrus. The hand service method could provide satisfactory lambing rates as effective as natural-service method in ewes for out-of-season breeding.
