Forty Romney hoggets were immunised against oestrone during March. A similar number served as untreated controls. Half of each group was treated with progestagen sponges to induce oestrus. Their ovulation rates were determined 7 day after sponge withdrawal and in mated hoggets within 14 days of first oestrus. Half of the immunised ewes were boosted as 2- and 4-tooths, the balance receiving only a 4-tooth booster. Half of the untreated controls were first immunised as 4-tooths. Ovulation and lambing rates were recorded. Immunisation increased hogget multiple ovulation rates by 50%. Unboosted 2-tooth ewes had multiple birth rates and numbers of lambs born similar to untreated controls. Boosted 2-tooths had more multiple ovulations (37%), ewes lambing multiples (28%) and lambs born (28%) than control ewes. The ovulation rate of 4-tooth ewes was 2.24. Untreated control ewes had the lowest proportion of triple ovulating ewes (11%), with first treated 4-tooths and 4-tooths missing their 2-tooth booster intermediate (22%) and annually boosted 4-tooths highest (38%). Control 4-tooths lambed fewest multiples (53%), first treated 4-tooths were intermediate (63%) and 4-tooths missing their 2-tooth booster and annually boosted 4-tooths highest (75%). However, differences in 4- tooth ovulation and lambing responses were not significant. The limited data demonstrate that annual immunisation against oestrone can increase ovulation and lambing rates. Ewes missing an annual booster perform at levels similar to untreated control. Furthermore, the immunomemory system for oestrone appears to last for at least 24 months since the ewes gave birth to 189% of lambs compared to 194% in annually boosted ewes and 159% in untreated controls.
Proceedings of the New Zealand Society of Animal Production, Volume 45, , 181-183, 1985
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