Out-of-season Breeding Alternatives for Sheep
Published on: 07/29/2008
Author : Delma Kennedy - Sheep Specialist, Genetics, Reproduction and Performance Programs/OMAFRA - Government of Ontario Ministry of Agriculture, Foods and Rural Affairs Fact Sheet
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 period of time; some breeds and individuals will cycle throughout the year. Prolific breeds and breeds that originated closer to the equator tend to be less seasonal.
Out-of-season Breeding Methods
Breed and Selection
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.
Genetic selection is a slow but permanent method of achieving breeding out of season. The trait has a low heritability (10%). This means it is difficult and time consuming to develop a flock of animals with the genetic ability to breed (naturally) on a year round basis. In order to create a selection program that works, it is necessary to define what out-of-season means.
* 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
* Is the ewe expected to breed out of season as a ewe lamb?
* How many daughters must a ram produce to be considered proven as an out-of-season breeder?
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 its own.
Modifications of day length can be used to 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 commences. 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. Breeds with a shorter natural season should be exposed to extended light and decreased light for a longer period of time. It is recommended that ewes be exposed to long days for 8-12 weeks and then exposed 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, it is recommended that 12 weeks be used for the best results. Rams as well as ewes should be exposed to the lighting regimen. Exposure of rams to short days will increase testicular growth, mating activity and semen quality.
There are several management factors that must be observed in the management of the light control system. The difference in illumination between short and long days should be 6-8 hr. 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, but will usually be a minimum of 8 weeks after the short days begin. The short day period should end as soon as the rams are removed from the ewes.
If all protocols are rigidly observed, conception rates of over 80% can be achieved if there is a minimum of 70 days between lambing and breeding. Ewes under this system will exhibit more than 1 estrus cycle similar to ewes breeding in season. 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 ewes should be exposed to long days, a producer needs to work backwards from the desired breeding date. The following example helps with the required calculations.
Desired Date Breeding Begins - May 15
Short Day Period (8 weeks) Begins - March 15
Long Day Period (12 weeks) Begins - December 15
There are 2 options for hormone control, vaginal pessaries (sponges) or melengesterol acetate (MGA).
Progestagen impregnated intravaginal sponges are inserted in the vagina for 12-14 days. At the time of sponge removal, the ewes are treated with Pregnant Mare Serum Gonadotrophin (PMSG). The ram is introduced to the ewes 24 hr after sponge removal when most ewes should be in heat. All ewes should be in heat after 48 hr. The fallout rate of the sponges is variable from farm to farm and season to season. There is a risk of vaginal infection or injury if the operator is not gentle and proper sanitation of equipment is not observed. Sponging isn't recommended for ewe lambs, primarily due to the risk of injury. Sponging is the best method of synchronization for artificial insemination (AI) because the time of ovulation can be more accurately predicted.
Sponges and PMSG can be obtained from a veterinarian. The results that producers see with this method can range from 8%-85%. The typical or average results are 50%-60% of the ewes treated having lambs out of season. Sponging results in only one synchronized estrus. It is not normal for sponged ewes to exhibit a second cycle out of season.
Melengesterol acetate 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 required.
MGA is fed at a rate of 0.125 mg, twice a day for 12-16 days. The MGA can be formulated into an ewe supplement or into a complete ration. The 2 feedings should be as close to 12 hr apart as possible. It is important to keep the hormone levels in the blood as consistent as possible. Similar to the sponges, give PMSG as part of the hormone treatment. Administer PMSG 5-10 hr after the last feeding of MGA. The timing of the MGA feeding and administration of PMSG must be strictly adhered to for good results. The ewes will come into heat 2-2½ days after the last feeding of MGA. Introduce the ram after 48 hr.
Similar to sponging, there is a wide variation in the results of using MGA, with reports of 10%-85%. The typical or average results again are similar to sponging at 50%-60%.
Management Factors Affecting The Success Of Out-of-season Breeding
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 during breeding. The start and duration of flushing depends on the body condition of the ewes. Flush thin ewes starting 2 weeks prior to the hormone treatment. Flush ewes in good condition starting when the hormone treatment begins. Continue flushing for 2-4 weeks after mating depending on body condition. Flush ewes until they are body condition score 3-3.5.
Minimize, or avoid, stress and handling during treatment, mating and for 1 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.
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 7-8 weeks. As a result, supplementary feeding must begin 8 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 2 months prior to breeding and ensure that all wool is removed from the scrotum. Another very important factor is to 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 5 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, sponges and MGA are all successful alternatives to enhance an out-of-season breeding program.