Tuesday, December 6, 2011

Embryo Transfer

Embryo transfer is the advance technique in animal breeding whereby a sexually mature female referred as donor is injected with exogenous hormone to produce more ova which is fertilized inside her by natural or artificial service are removed evaluated and transferred into the reproductive tract of surrogate mother where it is develop naturally into mature calf.
The history of embryo transfer is not too much longer. First embryo is transferred experimentally in 1949. The first embryo calf is produced in 1951 in England. Commercially embryo transfer technology is not used until 1970. In 1970's calf is produced industrially through the application of embryo transfer. And European dual purposes breed of cattle became popular with in short period of time. Day by day ET technology developed through different technique include artificial insemination, surgical recovery of embryo, rapid development of superovulation technique etc. After 1977 the embryo transfer technique became popular all over the world.

Embryo transfer is based on the development of genetic makeup of the progeny by insertion of either frozen semen or semen from genetically valuable bull into the donor which is also genetically superior. Then after fertilization embryo is transferred into surrogate mother which gives only physical support to the embryo.
Embryo transfer technique is involved many steps. Those are given below
1. Selection of donor.
2. Selection of recipient.
3. Management of donor and recipient.
4. Superovulation and synchronization of estrous.
5. Estrous detection.
6. Preparation of materials.
7. Insemination of the donor.
8. Collection of embryo (either surgical or non surgical method).
9. Handling of embryo (identification, evaluation of embryo).
10. Storage of embryo.
11. Transfer of embryo.
Selection of donor
There are two broad criteria that have to follow. One criteria is donor have to proven genetic value. A Second criterion is donor must have high reproductive rate. Beside these donor have to fulfill the following criteria:
- Donor should be free from reproductive disease.
- Proven genetic value containing cow are used as donor.
- Donor should have high reproductive rate.
- It should not be over fated.
- Donor should be healthy, regular cycling and a history of high fertility.
- Donor should not losing weight
- Non pregnant cows are usually referred to as donor.
Selection of recipient
Recipient cow selection is an important task for embryo transfer technology. Recipient cow must be fulfilling some basic criteria. Not all cows are able to be a recipient cow. Palpation must be done before selecting the cow or heifer as a recipient. It is done by putting the hand into the cow's bottom and try to fell around to see whether everything is in working order or not. Some cows have calving problem, twisted cervix so it is best to avoid these cows as recipient through the palpation of cow.
The feature of recipient cows are almost like donor but they need some extra criteria this are given below
- Less productive milking cow.
- Fertile and high capacity to conceive in AI programmer.
- Young cows for non-surgical transfers and heifers for surgical transfer programmes etc are used as recipient in embryo transfer.
Management of donors and recipients
Donors are managed in both the farm condition and embryo transfer center. But surrogate mother needs extra care in a care center. But both the cows need some basic equipment common such as chutes and head catches, refrigerator for keeping drug and an appropriate site to work with embryo.
Skilled person are needed for estrous detection, palpation, and AI. Health management programme should be available like vaccination, quarantine for incoming animal and testing programme.
Adequate physical facilities like feed storage are needed. Food planned nutrition programmes, record keeping system are also essential for the proper management.
Superovulation and synchronization of estrous
Once the recipient cow and donor cow are selected the first step is to superovulate to produce multiple ova (eggs). To do this donor cows are treated with the gonadotropin (hormone) like follicle stimulating hormone (FSH) twice daily for 4 days in the range of 8 to 14 days of estrous. So more eggs are released from each follicle then a low dose of prostaglandin F2 alpha is treated after 2-3 days later. Different types of hormone are used for the superovulation like PMSG, FSH, HCG, GnRH, Estradiol-17 B, prostaglandin F2 alpha etc.
Estrous detection
Estrous detection is very important and skilled person is needed for the detection. It's detected visually at least twice each day early in the morning and late in the evening. The detection of estrous is done by the following way---------------
- Move around in each cow for 10-15 min and observed carefully in a close contact.
- Suspicious sign for estrous is restlessness, bawling, nudging, mounting, sniffing, tail raising, discharge of clear mucus from the valve, swelling, inflammation of the valve etc.
- A calendar should be kept contain all records of donor and recipient. At the 18-24 days of estrous observe closely for estrous detection.
- Met estrus bleeding blood from valve are also the major detection sign of estrous
Insemination of the donor
Insemination of the donor is done either by natural mating with proven bull or by artificial insemination. Artificial insemination means insertion of semen from proven bull for fertilization artificially where by semen is also collected from bull artificially.
Collection of embryo
Embryo is collected from the donor by surgical or non-surgical method. But it is recommended that non-surgical method than surgical method. The recovery by non surgical method is really simple and done at approximately seven days after breeding. It needs only one hour. But a skilled persons and adequate equipments are required for this process.
Handling of embryo
Recovered embryos are needed to evaluate for stage of development and quality of the embryo under the microscope. After collection the embryo are usually in the morula stage and become blastocyst stage. The embryo then classified in a broad categories like excellent, very good, good, poor, very poor etc. Normally excellent, very good, good categories of embryo are selected for embryo transfer programme.
Storage of embryo
Selected embryos are preserved through cryopreservation at very low temperature. The embryo is frozen to extremely cold temperatures, using liquid nitrogen. At cold condition nitrogen exist in liquid form under these specialised conditions the embryos can remain dormant until such time when pregnancy is desired.
Transfer of embryo
Transfer of embryo is done by two methods surgical and non-surgical. But again non-surgical method is more effective. It is much easier to transfer embryo to the uterus than to the oviduct trough the non-surgical method.
Application of embryo transfer
• Very low risk of disease transmission.
• Increase reproductive rate of genetically valuable female.
• Obtain offspring from genetically valuable but infertile cow
• Easy to import and export.
• Used in MOET programme successfully.
• Cost of embryo transfer is not high.
• Passive immunity from native dam.

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