Five groups (15-30) of Romney or Merino ewes were synchronised with CIDR devices for 12 days in March or April. In all but one group of Romney ewes 400IU PMSG was injected at CIDR removal. Intervals to onset of oestrus and ovulation were determined by recording crayon marks and laparoscopy respectively every 4 hours. Interval to ovulation was not affected by ewe breed or month of treatment, but it was 7.9 hours earlier in ewes injected with PMSG (48.9h vs 56.8h P<0.001) and the variance was less (13.4h vs 35.7h P<0.05). Interval to oestrus was affected by breed of ewe, date of synchronisation and use of PMSG.

WJ, Parker, DI Gray, ST Morris, and SN McCutcheon

Proceedings of the New Zealand Society of Animal Production, Volume 52, , 221-224, 1992
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