Selection and preparation of recipient females
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 be on a proper plane of nutrition (body condition score 6 for beef cows and dairy body condition score 3 to 4 for dairy breed recipients.) These cows also must be on a sound herd health program.
A tough question to answer is: “How many recipient cows are necessary?” To establish an average figure for the number of embryo transfer calves from a single donor cow in a year is difficult. Variations in conditions are wide, but if a cow is flushed every 90 days over a 12 month period and five pregnancies are obtained per collection, an average of 20 pregnancies per year could result. Some cows have produced more than 50 pregnancies per year by embryo transfer and probably could have produced more if it had economically feasible. In the Louisiana study previously mentioned, the average number of embryos found per cow was 7.4. With only 58% of these being transferable, the average was 4.3 transferable embryos per flush.
To maximize embryo survival in the recipient female following transfer, conditions in the recipient reproductive tract should closely resemble those in the donor. This requires synchronization of the estrus cycles between the donor and the recipients, optimally within one day of each other. Synchronization of the recipients can be done in a similar manner and at the same working time as the donor cows. Injectable prostaglandin products are available from veterinarians and should be injected into the recipient at the same time they are injected into the donor cow. This optimizes the probability that the recipient will be in the same stage of the estrus cycle as the donor when transfer takes place. The “Syncro-Mate-B” system, which involves injecting the recipients and implanting them with a synthetic progesterone, also has been used successfully. The implant is removed nine days after its insertion, and the cows will show standing estrus approximately 30 to 40 hours later. This timing again must match the time of insemination of the donor cow so that the donor and the recipients have a similar uterine environment seven days later when the transfer takes place. Synchronizing drugs only are effective on recipient females that are already cycling. “Anestrus,” or non-cycling, cows that are too thin or too short in postpartum days will not make useful recipients.
Transfer of the embryos
The transfer of the embryo into the recipient cow first requires “loading” of the embryo into a 1/4-ml insemination straw. This is done under microscopic viewing, with the aid of a 1-ml syringe and requires considerable practice, patience, and dexterity. Degenerated or embryos of very low grade need not be loaded and can be discarded. Just prior to embryo transfer, the ovaries of the recipient are palpated rectally to determine which ovary has ovulated. With the aid of an assistant to hold open the vulva of the recipient cow, the transfer gun or insemination rod is carefully passed through the cervix. The tip of the rod is then allowed to slide into the horn on the same side of the ovary with an active corpus luteum. The embryo is gently expelled in the forward tip of that uterine horn. Great care is taken to not cause damage to the lining of the uterus. Such inflammation and scarring would greatly ANSI-3158-4 Oklahoma State University, in compliance with Title VI and VII of the Civil Rights Act of 1964, Executive Order 11246 as amended, Title IX of the Education Amendments of 1972, Americans with Disabilities Act of 1990, and other federal laws and regulations, does not discriminate on the basis of race, color, national origin, sex, age, religion, disability, or status as a veteran in any of its policies, practices or procedures. This includes but is not limited to admissions, employment, financial aid, and educational services. Issued in furtherance of Cooperative Extension work, acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, Samuel E. Curl, Director of Cooperative Exten- sion Service, Oklahoma State University, Stillwater, Oklahoma. This publication is printed and issued by Oklahoma State University as authorized by the Dean of the Division of Agricultural Sciences and Natural Resources and has been prepared and distributed at a cost of 20 cents per copy. 0902 reduce the probability of the pregnancy being established. Embryo flushing and embryo transfer are both done after an epidural anesthetic has been given to block contractions of the digestive tract and aid in the ease of manipulation of the cervix and the uterine horns. Embryos can be transferred immediately upon recovery and evaluation or may be stored frozen in liquid nitrogen and transferred at a later date. The freezing and thawing process also is also very intricate and usually results in an approximate 10 - 20% reduction in pregnancy rates from those observed with fresh embryos.
Frozen embryos are a marketable commodity and have been especially useful in international sales of United States beef and dairy genetics. Producers in this country who believe that they own cattle with the genetic capability to be valuable in other nations may wish to contact their State Department of Agriculture and ask about regulations and marketability of frozen embryos from their herd. Different nations have different health requirements of cattle producing frozen embryos for import into their country. Therefore, individual inquiries are necessary to learn what health and legal requirements are expected.
Non-surgical extraction of embryos is performed by the following way. A flexible catheter with an inflatable cuff is inserted into the vagina and through the cervix in one of the horns of the uterus. The cuff is inflated and closes the caudal exit of the horn of the uterus, thereby restricting a washing cavity. The catheter can be two-channel, which allows flow through the washing liquid. When using a single-channel catheter, the wash fluid is injected several times (5-8 times) and then flows out of the horn of the uterus. In both cases 200-300 ml of Dulbecco's phosphate buffer are introduced. Most optimal time for the extraction of embryos - 6-8 day after the start hunting, since early blastocysts of this age are most suitable for deep freezing and can be highly effective transplanted non-surgically. The donor cow is 6-8 once a year, extracting 3-6 embryos.
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