Effects of times of PMSG injection and ram introduction on estrus incidence and lambing rate in ewes treated during the non-breeding season.
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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.<BR>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.<BR>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 (<I>P</I><0.05).<BR>3) Semen characteristics and increased times of services did not affect lambing rates and prolifi-cacy in the 4 rams used.<BR>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.
- 日本繁殖生物学会の論文
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