Developments in Embryo Transfer in ewes
Breeders of pedigree sheep, such as Texel, Beltex or Suffolks, often use embryo transfer to aid breeding. Embryo transfer is an effective method of increasing the numbers in a flock and is also used to speed up the genetic improvement of a breed. Embryos are collected and transferred from pedigree ewes to recipient ewes. A specialised veterinary procedure is used whereby hormones are injected into the pedigree ewe to increase egg production. A surgical technique is then preformed where the fertilised embryos are flushed from the pedigree ewes by penetrating the abdominal cavity and flushing the oveducts. The embryos can then be transfered to surrogate mothers.
This technique enables the breeder to obtain lambs from ewes that either would be unable to carry otherwise, or it simply allows them to increase the numbers of lambs born in a breeding season. In most cases the recipient ewe is a common sheep who acts as surrogate mother to the pedigree lamb. The recipient ewe should be a proven, regular breeder, who is fit and is in good health. It is also important to have good milk production and mothering qualities.
In 1964, two breeders named Moore and Shelton did a study on embryo transfer in sheep. They reported that eggs transfered during the first three days after oestrus (the period during the ewe's reproductive cycle, best monitored using an oestrous detector) developed most sucessfully. Moore and Shelton showed breeders the most effective ways to use embryo transfer, with over 75% of all recipients becoming pregnant. Embryo transfer has developed further since Moore and Shelton's days, with specialised centres now being run to aid breeders with rearing pedigree flocks. Frozen sheep embryos are stored for purchase by breeders (even cross-nationally) and the entire embryo transfer procedure can now be done on the farm. This helps to reduce the risk of disease and also increases the chance of pregnancy. It also means that ewes can be flushed outside the main breeding season and their embryos frozen for use the following year.
In conclusion, embryo transfer has many uses and has been sucessfully developed to aid breeders with rearing many generations of pedigree sheep. The technique is not exclusivly used on sheep - goats and deer are also commonly breed in this way.