Bovine Embryo Transfer

Embryo transfer (ET) technologies are tools for advancing the rate of genetic improvement. Artificial insemination (AI) allows the rapid genetic improvement of a breed through the use of superior sires; embryo transfer is a means to increase the contribution made by superior females. This means that a greater percentage of the herd can be derived from valuable females than would be the case if only AI were to be used.

ET is widely used in the beef and dairy industries. ET is a cornerstone of many breeding programs and has allowed many breeders to excel. However, ET is not necessarily only for breeders of pure-bred animals. Many high producing grade dairy cows animals in the United States have been used as ET donors. ET is an involved process and attention to many details is important. In the 20 years since ET has become commercially viable, many changes have occurred in embryo collection, transfer, freezing and thawing processes.

York Animal Hospital offers an “on farm” embryo transfer program. In addition, “on farm” embryo freezing is available and can complement the embryo transfer procedure. With “on farm” work, it is the owner’s responsibility to superovulate the donor cow, provide the recipients and the facilities. This will be done under the direction of York Animal Hospital personnel.

Bovine Embryo Transfer

Embryo Transfer is an ever changing and expanding field. The commercial embryo transfer industry in North America developed in the early 1970’s with the introduction of exotic European breeds of cattle. Embryo transfer is basically used to exploit the genetics of the female in the same way that frozen semen was used to exploit the genetics of the male. As ET technology developed and improved, embryo transplant became more commonplace and affordable. It was used for genetic improvement rather than for increasing numbers of a particular breed or phenotype. Today it is the main method of moving genetic matings around the world.

Embryo Donor Selection:

There is no way of pre-determining how a donor will respond to super-ovulation or how many useable embryos she will produce. To improve the odds of a successful flush a donor that has calved 50-90 days and has a good reproductive history and relative youth will be your best bet. Donors should be on an increasing plane of nutrition with no specific nutritional deficiencies. Cows with moderate body condition scores preferred. Overfat cows generally create problems. Virgin heifers and cows that “come up open” are less predictable.

ET should be limited those cows with superior genetic merit. Just because the letters “ET” are in an animals registered name, it doesn’t make them genetically better or worth more money. ET is a great way to disseminate genetics of the “elite” cows. It will also disseminate undesirable genetics, so make sure your donor is free of known genetic defects.

When purchasing a proven donor cow, check her history of embryo production and calving history. Good donor cows tend to repeat as good donors whereas cows

Expected Embryo Transplant Results:

The most often asked question is “how many embryos can I expect from my flush?” The answer is “from zero to eighty”. Embryo production varies greatly from donor to donor and flush to flush. Average production is approximately 6-8 transferable embryos per super-ovulation. Remember, averages are made up of any combination of numbers, including zeros.

Pregnancy rates vary from flush to flush with fresh averages 60-70% and frozen 50-60%. Many factors affect pregnancy rate such as embryo quality, recipients, technical ability, and donor. Some donors consistently produce embryos with higher pregnancy rates that others with embryos of similar grade. This last factor seems to be uncontrollable and unpredictable.

Donor Sire Selection:

Today frozen semen is available from a large number of sires. Choose a sire that meets your genetic and phenotypic criteria. High quality semen is a must. If there is any question about the semen quality have it tested by qualified personnel.

Embryo Recipient Selection:

Proper recipient herd management is critical to embryo transfer success. Cows that are reproductively sound, that exhibit calving ease, and that have good milking and mothering ability are recipient prospects. They must also be on a proper plane of nutrition. These cows also must be on a sound herd health program.

Embryo Transfer Program

York Animal Hospital offers an “on farm” embryo transfer program. The program is completely non-surgical for embryo recovery from the donor(s) and transfer of embryos to recipients. In addition, “on farm” embryo freezing is available and can complement the embryo transfer procedure. With “on farm” work, it is the owner’s responsibility to superovulate the donor cow, provide the recipients and the facilities. This will be done under the direction of York Animal Hospital personnel.

Basic facility requirements are a heated barn or shed with running water, restraining chute, pens, and a reliable source of electricity. York Animal Hospital provides a mobile laboratory for handling embryos thus eliminating the need for a special room on the farm for microscopic and freezing work.

Keeping accurate records and constant attention to detail is absolutely necessary in embryo transfer work. If there are any questions regarding any aspect of the program, it is imperative that you contact the personnel at York Animal Hospital.

IMPORTANT ASPECTS OF EMBRYO TRANSFER PROCEDURES

1. A clearly legible ear tattoo or tag number must be present in donors and a certificate of registration with the appropriate breed association must be in the owner’s possession in beef and dairy breeds.
2. All recipients should be identified with large, easily visible ear tags. Health requirements (ie, blood tests) will depend on your particular situation and these should be discussed well in advance of embryo transfer work.
3. Observe and record heat dates in recipient animals to be used in embryo transfer programs for as long as possible in advance to ensure that they are cycling normally prior to embryo transfer.
4. Both donor(s) and recipient animals should be on a rising plane of nutrition, especially if they are nursing calves.
5. Following calving, donor(s) should show two heats before superovulation treatment. Similarly, the recipients should have had at least two heat cycles prior to receiving embryos.
6. Donor superovulation will begin on Day 4 of the treatment program and Folltropin injections must be given twice daily by deep intramuscular injection at 12-hour intervals (8:00 am and 8:00 pm) for four days. A detailed superovulation schedule to be followed will be provided by York Animal Hospital prior to commencement of treatment.
7. The Folltropin hormone used in superovulation of donor animals comes as a dried powder and must be dissolved in the sterile water solution provided prior to use. The Folltropin solution must be refrigerated between injections. A new sterile syringe and needle must be used for each injection.
8. The recipient animals must be injected with prostaglandin 12- 24 hours before the donor(s). Depending on the donor treatment schedule provided, the recipient animals will receive prostaglandin intramuscularly on Day 6. Donor(s) will receive prostaglandin on Day 7. Both donor(s) and recipients should be in heat on the morning of Day 9. Heat signs may occur earlier in the donor (ie, evening before the anticipated date). Any deviations should be reported to York Animal Hospital.
9. It is extremely important that the donor and recipients be closely observed for first signs of heat and the time of onset of heat be recorded. Recipients must be in heat within 24 hours of onset of heat of donors for best results.
10. Breeding of the donor cow should occur three times at 12-hour intervals.
11. Palpation of the superovulated ovaries at the time of heat and artificial insemination of the donor is strongly discouraged.
12. An empty container (straw or vial) of bull semen must be saved for York Animal Hospital to record bull’s name, I.D., registration number, batch number and freezing date on embryo collection forms. Please record date and time of services of donor cow. If the breeding is done by an A.I. technician in your area, please obtain breeding certificates. It is strongly advised to have frozen semen evaluated prior to use in donor cow programs.
13. Approximate number of recipients to synchronize for donor(s) program:
    • One donor – 8-12 recipients
    • Two donors – 12-19 recipients
    • Three donors – 18-25 recipients
    • On the average 20 to 30% of the recipients will not be used because of synchronization failure.
14. Donor collection and recipient transfer can be done 6, 7 or 8 days following onset of heat. Donor collection on Day 7 is preferable, especially if complemented with embryo freezing.
15. At collection time, a mobile laboratory will be provided for embryo handling. The donor cow can be restrained in a trimming chute or squeeze chute for collection. A squeeze chute is preferred to restrain the recipients for non-surgical transfer. Portable panels can be used to make a runway leading to the squeeze chute. The whole arrangement can be located in a calving barn or shed.
16. Method of payment for travel, embryo recovery and transfer must be agreed upon prior to collection of the donor.
17. Embryo transfer certification will be mailed to you once accounts are paid.

In summary, pregnancy rates are variable and relate to donor, recipient, embryo and operator factors, many of which may interact, usually negatively, to influence the outcome. Clients thinking of an ET program should be prepared to follow directions explicitly. There are no guarantees and careful attention to detail is important to reduce the chances of a program being disappointing and increase the probability of it being remarkably rewarding.

Please discuss your breeding programs and your expectations for embryo transfer with us, and stay in touch with us once the embryo transfer program is initiated. Please note the telephone numbers above; contact us at any time if you have any questions or concerns.