Typically, I focus on a health-related topic that is helpful for the time of year which troubles are usually experienced, but recently I had a producer request an article on embryo transfer. I often use a little phrase, “I’m pretty good at diesel engine repair and embryo transfer, but not so good at computers”, so let’s have a look at embryo transfer and some tips to set your cows up for success.

Potential for Offspring

In a typical breeding program, live cover or artificial insemination, the most calf(s) you can expect would be two in the case of twins (exception for triplets!). However, with multiple ovulation embryo transfer (MOET) there would be the potential of multiple calves from one donor. With MOET, a donor is selected and treated with twice daily doses of follicle stimulating hormone. The follicles which normally undergo atresia are ‘rescued’ and the donor ovulates multiple oocytes. Then semen of your choice (genetically high value, sexed) can be used to artificially inseminate the donor.

Embryo Flushing

The best results for flushing embryos will be 7 days post breeding. In the cow, embryos leave the oviduct and enter the uterus at 3-4 days post fertilization. From this point the embryo continues to grow to a morula or early blastocyst on day 7. The flushing process is relatively simple as a Foley catheter is passed through the cervix into the uterine body and a cuff is inflated to allow filling of the uterus and prevents spilling of the media. Once the uterus is filled, the fluid is then retrieved and passed through a filter to collect the embryos. The filling/retrieval process is repeated several times and then the dish is searched for embryos. Once the embryos are removed from the dish and placed in a holding/wash media, the quality of the recovered embryo is graded for likelihood of success. Grades are 1-4 with 1&2 considered the best for freezing or transfer.

Transfer to Recipient

This process is very similar to AI except for the rod used to place the embryo. The rod is ¼ inch and is several inches longer than a typical AI gun. Where the uterine horn makes a difference as well. With AI, the semen is deposited into the uterine body. With ET, the embryo must be placed in the same horn that has a corpus luteum (CL) on the ovary. Also, research has shown that placing the embryo at least 2/3rds down the horn has improved pregnancy success rates.

Pregnancy Rates

Of course, pregnancy rates and embryo recovery are going to vary. The reported average recovery rate is anywhere from 6-8 transferrable/freezable embryos per flush. One case in point is an experience of my own. A producer brought 2 Jersey cows for me to flush. Same age cows, same products, same set of circumstances. One cow yielded 20, while the other had 2. Pregnancy rates vary with fresh transfer reported at 60-70%, and frozen 50-60%. Pregnancy rates can be influenced by embryo quality, technician experience, and recipients’ selection.

Factors for Success

Donors and recipients can influence success rates. Some factors to consider are:

Donors

• Choose females that start estrous cycles at a young age
• Typically conceive with >2 breedings
• No reproductive abnormalities or history of dystocia
• Genetically tested for any potential defects
• Even though the female has been super ovulated, ensure that she responded to the protocol by palpation of the ovaries for CLs. There is no need to even start a flush if the donor did not respond.
• Use the same estrus synchronization protocol as the recipients.

Recipients

• It is recommended to use heifers as recipients.  Highly fertile, free of uterine disease, and in optimal body condition scores. Sex is a luxury, so ensure the donors and recips are in good health.
• Use the same estrus synchronization protocol as the donor. Because the embryo is transferred on day 7, the recip must be in estrus at the same time as insemination of the donor. It is preferred that the recip be slightly ahead of the donor, but +/- 24 hrs is acceptable.
• Ensure that the recip has a suitable CL (~18-20 mm) for transfer. This should be done before the embryo is thawed or fresh transfer.
• The embryo gun should have a guarded sheath to protect the gun as it passes through the vagina.
• The process should be as gentle as possible. If the gun is traumatic to the endometrium (lining of the uterus) prostaglandin will be released which lyses the CL and removes progesterone to maintain pregnancy.
• Most veterinarians will give an epidural and Banamine^® to reduce inflammation.
• Avoid high ambient temperatures when transferring. Extreme temperatures lower fertility

I realize that MOET may not be for every operation, but I hope this information helps with any decisions that you may make or improve the success rate if you are utilizing MOET already! If you have any questions, please reach out to your veterinarian, Extension agent, or me.

If you have any questions, please feel free to reach out: https://animalscience.tennessee.edu/ask-dr-lew/