Out-of-Season Breeding Alternatives for Sheep
Table of Contents
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.
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. 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:
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.
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.
There are several management factors to observe in managing the light control system.
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 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 to expose ewes to long days, work backwards from the desired breeding date. The following example helps with the required calculations.
Desired Date Breeding Begins - May 15
There are two options for hormone control: controlled internal drug release devices (CIDRs) or melengesterol acetate (MGA).
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.
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.
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.
Treatment of Ewes
The management and care of the ewes has a large impact on the success of out-of-season breeding.
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.
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.
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