Ram induced stimulation of ovarian and oestrous activity in
anoestrous ewes - a review
T.W. Knight
Whatawhata Hill Country Research Centre, Ministry of Agriculture
and Fisheries, Hamilton
Proceedings of the New Zealand Society of Animal Production.
1983, 43: 7-12
The stimulation of oestrus in ewes early in the breeding season
has been known for a number of years but only recently has there been a
full understanding of the changes which occur in the ewe. Recent work
indicates that only 17 to 21 days isolation from rams is needed to
sensitise ewes to the ram. Within 10 minutes of introducing rams, the
luteinising hormone (LH) levels increase in the ewe. This can result in
a preovulatory LH surge 27 to 35 hours later and a silent ovulation
within 54 to 72 hours in anovular ewes. However, 43 to 59% of ewes have
a premature regression of the corpus luteum (CL) and a second silent
ovulation occurs 4 to 6 days later. This leads to flocks have peaks of
first oestrus around days 18 and 24 after ram introduction. Injection
of progesterone at ram introduction prevents premature regression of the
CL and first oestrus is synchronised over days 19 to 21 after ram
introduction. The percentage of multiple ovulations is higher at the
silent ovulation than at the first oestrus or in spontaneously ovulating
flock mates. Priming with progestagens for 12 to 16 days can induce
oestrus at the first ovulation after ram introduction and still maintain
the increased proportion of multiple ovulations.
The ram effect is due to pheromones which are present in the ram's wool
and wax. The buck is as effective as the ram at stimulating ewes and
fatty acid pheromones isolated from the buck are also effective at
stimulating ewes.
Keywords: NZSAPAB;
Ewes; pheromones; ram stimulation; silent ovulations; anoestrus
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Last Updated 03-05-1997
