It is becoming more and more common for shepherds to consider how to manipulate the
breeding season in their flocks to reduce the number of sleepless nights at lambing.
Almost all sheep breeds are traditionally “short day breeders” with their breeding cycle
triggered by the time of year. Reducing sunlight hours increases the levels of the hormone
melatonin in the blood triggering the ewe’s ovaries to begin developing eggs and tup
testicles to producing more sperm.

There are numerous ways in which we can advance the breeding season or simply tighten
the lambing period which will be summarised below.

The Ram Effect – Teasers

The principle behind the “ram effect” is that the sight, smell and behaviour of a ram can
stimulate ewes to come onto heat or tupping. The optimum “ram effect” occurs when ewes
have been separated from the sight, sound, smell and by a minimum distance of one mile
from an entire male for a minimum of 2 weeks, but ideally 4 -6 weeks, before introduction of
a ram.
Due to the ‘ram effect’ ewes will come tupping or have a silent heat within 3 days of
introducing the ram, therefore, some ewes will be mated straight away but others will not be
receptive until 17 days later.
Teaser rams are those which have had a surgical procedure (vasectomy) to remove a length
of tube which carries sperm from the testicles to the penis. This makes them infertile while
still being able to produce testosterone so able to smell, sound and behave like an entire
ram.
If a teaser ram is used in the initial period when some ewes are receptive while others aren’t,
while the teaser is in with the ewes no animals that happen to come tupping will get
pregnant, instead all ewes will be receptive about 15-20 days after teaser ram introduction.
The general procedure for teaser tups is to introduce them to the ewes and after 14-16 days
replace them with entire rams. There are variations on this procedure but the principles are
the same and the most important factor for its success is that ewes are separated from all
rams prior to introduction of the teaser ram.

As the teaser needs to have his effect on numerous ewes it is recommended to limit 1
Teaser ram to 50 ewes; as all the ewes will have a heat in a fairly short period after teaser
removal the entire ram ratio should be 1 to 20 ewes.
Teaser tups should be prepared at least 6 weeks before they are needed as fertile sperm
can be held in the remaining cord for this time. Ideally a teaser should be turned with some
cull ewes before he is used to allow him to “empty out” any sperm remaining. Tups of any
age can be prepared but the “Ram effect” is best achieved by using mature rams.
Teaser tups can help bring ewes into season a week or 2 earlier than normal with a low
initial cost per ewe (the cost of an operation split across 50 ewes for 3 seasons). The
effectiveness of a teaser declines and ideally, he should be replaced after 3 seasons
although many are usable for several years.

Intravaginal Devices

Intravaginal devices such as sponges or CIDRS have multiple uses in sheep flocks. When
used in combination with PMSG they can advance the natural onset of tupping by up to 6
weeks, synchronise ewes before AI or to synchronise ewes for tupping.
Sponges and CIDRS are vaginal implants that are left in place for 12-14 days before being
removed and rams introduced after a set period, at a ratio of 1 mature ram to 10 ewes, ram
lambs will require less ewes to cover.
While in place the device releases progesterone which prevents the ewe coming tupping and
also allows eggs to develop, on removal of the device the progesterone level drops
triggering the onset of tupping and the eggs are then released.
As this happens in all ewes at the same time a tight service window is achieved and
subsequently this protocol is widely used to condense your lambing period down to around 3
weeks with a large proportion of ewes lambing within 5-7 days.
To achieve an advance on the natural breeding season, PMSG (a hormone injection) must
be given at the time of removal to ensure eggs are released. The number of eggs released
will depend on the dose of PMSG given so be wary in particularly prolific breeds and discuss
with your vet what a suitable dose will be factoring the breed of ewe, time of year, nutritional
status and past experiences.

Melatonin Implants

As discussed at the start of the article, short days cause an increase in the levels of the
hormone melatonin in the blood which in turn signals to the ewe the onset of the breeding
season. To advance the natural onset of the breeding season by approximately 6 weeks a
Melatonin implant can be given at the base of the ear, this will not synchronise the ewes or
tighten the lambing period.
Implants may also be given to rams and in the authors experience it can improve libido and
sperm quality earlier in the season particularly in breeds which normally mate later in the
season such as Blue Faced Leicester's. Implants should be given to ewes 5-6 weeks prior to
mating and in rams 8 weeks prior to mating.

Summary

This article gives you a good idea of the methods available to advance or synchronise the
breeding season in sheep flocks of all sizes, purposes and breeds.
Whichever method you choose it is vitally important to ensure that good husbandry is
followed in the lead up to tupping as you would do normally to ensure good success rates.
● Ensure you use the correct ram:ewe ratio for the method you have chosen.
● Ensure ewes are in appropriate Body condition score (2.5 for hill breeds, 3 for upland
breeds and 3.5 for lowland breeds).
● Ensure ewes and rams have the correct nutritional and trace element status.
● Flush ewes on a rising plane of nutrition to ensure good egg development.
● Abortion vaccines should ideally have been given at least 4 weeks before tupping.
● Ensure rams have passed a MOT (teeth, toes, testicles, tone, treat) and ideally been
fertility tested by your vet.