Factors influencing the time to onset of oestrus after
synchronisation treatment in ewes
J.F. Smith, J.A. Konlechner, J. Parr
MAF Technology, Ruakura Agricultural Centre, Private Bag,
Hamilton, New Zealand
Proceedings of the New Zealand Society of Animal Production.
1991, 51: 117-122
A series of four trials, each involving 1200 ewes have been
conducted over the period 1986 to 1990. Ewes have been treated with
various synchronisation treatments and the time to onset of oestrus
monitored each month of the year. Results indicate that while overall
mean values for each year don't differ, there were significant seasonal
effects within years with the interval to onset being shorter during the
breeding season. However, the maximum difference between monthly means
in any one year varied from 27 h to 17 h. Significant effects of
synchronisation device were seen with ewes treated with sponges having a
longer (+ 8 h) interval to onset than ewes treated with CIDR devices.
While effects of ewe age and ewe liveweight were seen in some trials no
consistent trend was identified. On most occasions significant
interactions with month of year indicated inconsistency of effect within
any one trial. The recorded variation in interval from device removal
to onset of oestrus is in agreement with that reported between flock in
the field. This variation is sufficient to effect conception rates to
artificial insemination performed on a time basis and evaluation of
contributing factors is required for the development of protocols for
this activity.
Keywords: NZSAPAB;
Synchronisation; oestrus; time to onset; ewes; Coopworth; CIDR;
sponge; PMSG
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Last Updated 25-01-1997
