A Review of Embryo Transfer Technology in Cattle
In animal husbandry, embryo transfer has become the most powerful tool for animal scientists and breeders to improve genetic construction of their animal herds and increase quickly elite animals. It is a technique by which embryos are collected from a donor female and are transferred to recipient females. It could send female and male genetics worldwide in a cryopreservation tank without the hassle and complications of exporting live animals and the associated risk. The success and economics of cattle embryo transfer programme is dependent on several factors; skill and experience of the embryo transfer operator, selection and management of recipient animals, close synchrony of oestrus between donor and recipient, quality of embryos transferred and methods used in embryo handling and transfer on the farm. The potential donor cow should be reproductively sound to produce maximal results. She should have a normal reproductive tract on rectal palpation and have a normal postpartum history, especially with regard to cycle lengths of 18 to 24 days. Superovulation of the cow is the next step in the embryo transfer process. Superovulation is the release of multiple eggs at a single estrus. Cows or heifers properly treated can release as many as 10 or more viable egg cells at one estrus. Approximately 85% of all normal fertile donors will respond to superovulation treatment with an average of five transferable embryos. Using high quality semen with a high percentage of normal, motile cells is a very critical step in any embryo transfer program. Early collection techniques involved surgically or non surgical removing the oviducts from live females at 72 hours post ovulation so that the embryos could be recovered by flushing. Recipients must have a proven reproductive performance, free of congenital or infectious diseases to obtain high conception rates and have a sturdy body size to avoid problems of dystocia. The transfer must be to a recipient in the same stage of cycle as the donor. For non surgical transfer, the deposition of the embryos in the uterus horn with corpus luteum is performed under rectal control with a transfer catheter similar to the technique of flushing for embryo collection. Success rates with embryo transfer in many commercial situations are consistently high, often exceeding 70% pregnancy rates. Non surgical embryo transfer techniques utilized today involve the use of an artificial insemination pipette and more recently, specialized embryo transfer pipettes. The intercontinental transport of a live animal is coasty. Where as an entire herd can be transported, in the form of frozen embryos, for less than the price of a single plane fare. There are several potential problems which must be overcome in order to make the international movement of embryos commonplace. Many factors may influence the embryo transfer technology that may be beyond the control of practitioners. Travel problems sometimes means traveling to a farm a day or two late, which mandates working with older embryos than planned. The risk of transmitting genetic disease via embryo transfer is the same as that involved in natural mating or artificial insemination. It is recommended the process for production, selection of donor and recipients, and transfer procedures of embryos as well as in recipient management will be needed to know before embryo transfer.
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