Effect of oestrogen pre-treatment and duration of CIDRÆ treatment on pattern of onset of oestrus in ewes

J.F. Smith, J. Parr

AgResearch, Ruakura Agriculture Centre, Private Bag 3123, Hamilton, New Zealand

Proceedings of the New Zealand Society of Animal Production. 1992, 52: 257-260

Two trials were conducted which examined the effect of duration of CIDRÆ device treatment on the pattern of onset of oestrus. Trial involved a total of 1,342 (Coopworth or Polled Dorset x Coopworth) ewes treated with either a CIDRÆ (type G) for 14 days and 400 i.u. PMSG at withdrawal, or a CIDRÆ for 10 days with 1.0 mg ODB at insertion and 400 i.u. PMSG at withdrawal. Observations were performed each month from February to August. Trial 2 conducted in April involved 4 groups of 50 Coopworth ewes and compared the 14 d CIDRÆ and 10 day CIDRÆ + ODB treatments both with and without PMSG at withdrawal.

There was a seasonal shift in the pattern of onset of oestrus in trial 1 with a shorter interval from device withdrawal to oestrus during the breeding season (March-June). The 10 day CIDRÆ + ODB treatment produced both a delayed pattern of onset in both trials and also a higher proportion of ewes not detected in oestrus. Ewe liveweight also influenced the pattern, with heavier ewes having an earlier onset of oestrus. The effect of PMSG in trial 2 was to advance the onset pattern but this was only apparent when combined with the standard 14 day CIDRÆ treatment.

Keywords: NZSAPAB; CIDRÆ, PMSG, ODB, oestrous synchronisation; Coopworth; Polled Dorset; time to onset of oestrus; liveweight; ewes; duration of treatment.

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Last Updated 25-01-1997