Reproductive response of mature and nulliparous yearling ewes to the ram effect during the non-breeding season

Sudden introduction of rams to ewes that remained isolated from males during the non-breeding season induces ovulation and thus out-of-season breeding. The aim of this study was to compare the reproductive response of mature and nulliparous yearling ewes to the ram effect during the non-breeding season. The experiment was performed during October November (mid non-breeding season) with 122 Merilin ewes 56 were mature multiparous (group ME) and 66 nulliparous, 1 year old ewe lambs (group HE) that previously remained isolated from males. All ewes were pretreated with intravaginal sponges for 6 days before the introduction of the rams. More ME than HE ewes ovulated (87.5 vs 66.7%, P < 0.01), and come into oestrus (66.1 vs 30.3%, P < 0.0001), and the ovulation rate was also greater in ME than HE (1.27 +/- 0.05 vs 1.10 +/- 0.04, P < 0.05). The pregnancy rate in the first oestrus period was also greater in ME than in HE ewes (39.3 vs 16.7%, P < 0.01). Overall, yearling ewes can respond to the ram effect ovulating and becoming pregnant during the non-breeding season. However, the reproductive response was lower compared with that of mature ewes. (C) 2016 Elsevier B.V. All rights reserved.