Breeding Alternatives for Sheep
Out-of-season breeding is becoming more popular as producers move to
accelerated-lambing programs to increase the supply of product to the
marketplace on a year-round basis.
Controlled reproduction will synchronize the ewes so that lambing occurs
in a restricted timeframe. It will also give an out-of-season heat so
that ewes can be bred in the spring for accelerated-lambing programs and
for the production of lamb for the Christmas and winter markets.
Sheep show estrus in late summer and
fall when day length is decreasing. During this period of the year, sheep cycle
approximately every 17 days (range 15-19 days). Some breeds will cycle or show
estrus for a longer time period; some breeds and individuals will cycle throughout
the year. Prolific breeds and breeds that originated closer to the equator tend
to be less seasonal.
There is a large variation between breeds in the length of
breeding season. The season for each breed tends to vary around the shortest day.
Breeds with longer breeding seasons will be more likely to breed out of season.
If the season for a breed is about 100 days long the season will tend to start
50 days before the shortest day and end 50 days after the longest day. If the
season is 70 days long, it will tend to start 35 days before the shortest day
and end 35 days after the shortest day.
Genetic selection is a slow but
permanent method of achieving breeding out of season. The trait has a low heritability
(10 per cent). This means it is difficult and time consuming to develop a flock
of animals with the genetic ability to breed (naturally) year round. In order
to create a selection program that works, it is necessary to define what out of
season means on your farm.
Some questions to consider:
- Is this
a ewe that will breed in April, May, June or July?
- Does the ewe have to
lamb out of season every time she is exposed to be considered an out-of-season
- Is the ewe expected to breed out of season as a ewe lamb?
many daughters must a ram produce to be considered proven as an out-of-season
The other problem that makes selection for this trait very
slow is that the trait is not expressed until the selected animal has lambs of
Modifying day length can induce sheep to ovulate out of season. The change
of day length from long days to short days initiates estrus. As a result,
it is necessary to create a situation with light control where long days
are followed by short days before the out-of-season breeding starts. This
can be done gradually or abruptly.
There are breed differences
in response to light control but most breeds will respond to a light control program.
- Expose breeds that have a shorter natural season to extended and decreased
light for a longer time period.
- Expose ewes to long days for 8-12 weeks
and then to short days for 8-12 weeks before breeding. If the out-of-season breeding
period is in June, near the longest days of the year, best results are obtained
by using 12 weeks.
- Expose rams, as well as ewes, to the lighting program.
Exposing rams to short days increases testicular growth, mating activity and semen
There are several management factors
to observe in managing the light control system.
- The difference in illumination
between short and long days should be six to eight hours. Flashes of light will
upset the ewe's perception of the period of darkness.
- A minimum of 100
luxes of light is needed for daylight and less than 10 luxes of light can be present
for the period of darkness.
- The time of the start of breeding after the
short days begin depends on the breed of ewe and the time of the year. This will
usually be a minimum of eight weeks after the short days begin.
- End the
short day period as soon as the rams are removed from the ewe.
If all protocols are rigidly observed, conception rates of over 80 per cent can
be achieved if there is a minimum of 70 days between lambing and breeding. Ewes
under this system will exhibit more than one estrus cycle similar to ewes breeding
If a light control system is undertaken it is important
to do everything possible to ensure success because ewes that don't breed out
of season (to the light control) will come into estrus the following fall 8-12
weeks later than usual.
To determine the dates when to expose ewes
to long days, work backwards from the desired breeding date. The following example
helps with the required calculations.
Date Breeding Begins - May 15
Short Day Period (8 weeks long) Begins - March
Long Day Period (12 weeks long) Begins - December 15
are two options for hormone control: controlled internal drug release devices
(CIDRs) or melengesterol acetate (MGA).
- Insert naturally
occurring progesterone impregnated CIDRs into the vagina for 12-14 days.
removal, treat the ewes with Pregnant Mare Serum Gonadotrophin (PMSG).
the ram to the ewes 24 hours after CIDR is removed, when most ewes should be in
heat. All ewes should be in heat after 48 hours.
- The fallout rate of
the CIDR varies between farms and seasons.
- There is a risk of vaginal
infection or injury if the operator is not gentle and proper sanitation of equipment
is not observed.
- CIDRs are not recommended for ewe lambs, primarily due
to the risk of injury.
- Using CIDRs is the best method of synchronization
for artificial insemination (AI) because the time of ovulation can be more accurately
predicted than when using MGA.
- CIDRs and PMSG must be obtained from your
The results that producers see with this method can
range from 8 per cent to 85 per cent. Typical results are 50 per cent to 60 per
cent of the ewes treated having lambs out of season. CIDRs generally produce only
one synchronized estrus out of season.
is a feed additive. It is commonly used in feedlot heifer rations to prevent estrus.
It is not licensed for use in sheep and therefore a veterinary prescription is
- Feed MGA at a rate of 0.125 mg, twice a day for 12-16 days.
- The MGA can be formulated into a ewe supplement or into a complete ration.
- The two feedings should be as close to 12 hours apart as possible. It
is important to keep the hormone levels in the blood consistent.
to the CIDRs give PMSG as part of the hormone treatment.
- Administer PMSG
five to 10 hours after the last feeding of MGA.
- For good results, strictly
follow the timing of the MGA feeding and administration of PMSG.
ewes will come into heat two to two-and-a-half days after the last feeding of
- Introduce the ram after 48 hours.
Similar to CIDRs, there is a wide variation in the results of using MGA,
with reports of 10 per cent to 85 per cent, with average results of 50
per cent to 60 per cent.
Management Factors Affecting the Success of Out-of-Season Breeding
Treatment of Ewes
The management and care of the ewes has a large impact on the success
of out-of-season breeding.
- Ewes must be in good body condition, preferably gaining body weight
at the time of mating. Feed the ewes a flushing ration prior to and
- The start and duration of flushing depends on the body condition of
the ewes. Flush thin ewes starting two weeks prior to the hormone treatment.
Flush ewes in good condition starting when the hormone treatment begins.
Continue flushing for two to four weeks after mating depending on body
condition. Flush ewes until they are body condition score
- Minimize, or avoid stress and handling during treatment, mating and
for one month after mating.
- If possible, mate ewe lambs separately from mature ewes. The rams
will preferentially mate mature ewes and ewe lambs tend to come into
estrus later than mature ewes following hormone treatment
Treatment of Rams
It is also important to ensure good care and management of the rams.
Poor nutrition can decrease testicular size and sperm reserves at a time
when the size and reserves are already smaller.
- Production of spermatozoa takes seven to eight weeks. Begin supplementary
feeding eight weeks prior to mating to increase sperm reserves.
- There are seasonal variations for rams in semen production, quality
and libido. Elevated body temperatures in rams from hot weather can
cause temporary infertility.
- Shear rams two months prior to breeding and ensure that all wool is
removed from the scrotum.
- Ensure that adequate ram power is available for out-of-season breeding.
Rams are not able to breed as many ewes out of season. It is recommended
that a maximum of five ewes to each ram be used out of season, particularly
when hormone treatments are used and the ewes are synchronized. Hormone
treatments can be staggered to optimize ram power.
Regardless of the out-of-season breeding method used, it is important
to ensure that ewes and rams are managed to optimize success. The breed
of the flock will affect the animals' natural season and the ability to
respond to controlled reproduction methods. Light control, CIDRs and MGA
are all successful alternatives to enhance an out-of-season breeding program.
This Factsheet was written by Delma Kennedy, Sheep Specialist - Genetics,
Reproduction and Performance Programs, OMAFRA, Guelph.