Embryo Transfer in Cattle

Introduction This slide show is a general overview of embryo transfer (ET) in beef and dairy cattle. It includes a brief discussion of the benefits and instructional methods of ET.

Introduction (continued) ET is a expensive procedure, costing around $300 for each flush and approximately $270 for each calf born. Students should understand that ET is a complicated procedure with a fairly high difficulty level. ET should only be performed by trained professionals. Teachers should remind students that this is only a brief overview of ET. Students will not be equipped with the knowledge and experience required for ET after the completion of this slide show. Further training is necessary.

Objectives Explain the benefits of embryo transfer. Briefly outline the procedure of embryo transfer.

Reproductive Anatomy The vagina, cervix, uterus, ovary, oviduct, and uterine horn should be pointed out to students. These structures will be discussed later in the slide show. Students should become familiar with the geographical location of each for a better understanding of ET.

What is an Embryo? An embryo is an egg that has already been fertilized by a sperm cell. It is an organism in the earliest stage of development.

What is Embryo Transfer? ET involves the removal of an embryo from a female of superior genetics and the placement of the embryo into the reproductive tract of a female of average genetics.

What is the Goal of Embryo Transfer? The goal of ET is to obtain the maximum number of genetically superior embryos in a minimum amount of time.

Benefits of Embryo Transfer Traditionally, cows produce only one calf per year. ET allows the production of many offspring within a year from a single cow.

Benefits (continued) ET can increase the genetic potential of a herd in a relatively short period of time. ET can increase milk production in dairy herds. ET can increase weaning weights in beef and dairy herds.

Benefits (continued) ET allows other producers to take advantage of superior genetics because frozen embryos can be shipped almost anywhere. ET preserves superior genetics for future generations due to embryo freezing.

Necessary Equipment for Embryo Transfer Plastic media bag Foley catheter Embryo filter

Necessary Equipment for Embryo Transfer (continued) Microscope Straw Rod

Necessary Equipment for Embryo Transfer (continued) FSH Prostaglandin (Lutalyse)

Necessary Equipment for Embryo Transfer (continued) Penicillin Lidocaine

Necessary Equipment for Embryo Transfer (continued) Plastic Sleeve Bull Semen

The Process of Embryo Transfer ET begins with the selection of a donor cow. The donor cows will contribute the embryos to be transferred.

Donor Cows Have Superior Characteristics High milking ability High growth rate Outstanding reproductive capacity

Bull Selection Next, a bull with superior genetics should be selected. Breeding can occur naturally or by artificial insemination.

Finally, recipient cows must be selected. Recipient cows serve as surrogate (foster) mothers to the calves, but contribute no genetic information. For this reason, the genetic makeup of the recipient cow is not as important as the makeup of the donor cow.

Recipient Cows (continued) However, the recipient cow must be able to maintain her pregnancy to term and produce an adequate milk supply for her calf. It is very important to stress to students that a recipient cow must have good milking ability. Other genetic traits aren’t as important, but the available milk supply to a newborn calf has a huge impact on the calf’s life.

Synchronizing the Estrous Cycle Once the donor and recipient cows have been selected, they must be synchronized so they are on the same phase of their estrous cycle. It is important to synchronize estrous cycles because the reproductive environments of the donor and recipients must be identical in order for the embryo to survive the transfer. Synchronization of estrous cycles is a complicated process and this slide show only goes into minimum detail. The important thing students should understand is that the donor and recipient cows must be on the same phase of their cycles for ET to be successful.

Synchronizing the Estrous Cycle (continued) The estrous cycle is controlled by the production and secretion of hormones at the proper time during the cycle. Prostaglandin (PGF2α) is the hormone used to synchronize the estrous cycles of the donor and recipient cows.

Synchronizing the Estrus Cycle (continued) Prostaglandin is produced naturally by the cow. However, a synthetic version called Lutalyse is given in one or two injections to synchronize estrous cycles. Lutalyse injections are given in 5cc doses, intramuscular, in the neck or hip.

Preparing the Donor Cow to be Flushed Before the donor cow is flushed, she is superovulated with a series of injections of Follicle Stimulating Hormone (FSH). Ovulation is the process of releasing eggs. Superovulation causes the ovary (the female reproductive organ) to produce many follicles. The word flush is introduced here. A flush is the process of removing embryos from the reproductive tract of the donor cow. Flushing in addressed in later slides.

Preparing the Donor Cow to be Flushed (continued) Follicles are small blister-like structures that develop on the ovary containing one egg each. When the follicles ovulate, the eggs are released. Superovulation ensures that many eggs will be released because there are many follicles present.

Breeding the Donor Cow When the donor shows signs of estrus (the time period during the estrous cycle when she will allow breeding), she is ready to be bred. Some signs of estrus are riding other cows, clear vaginal mucus, and pacing the fence. Take note of the two different spelling estrus and estrous. Estrus is the time period when the female will allow breeding. Estrous is the entire reproductive cycle from the beginning of one heat to the beginning of the next. Even though the pronunciation of both words is the same, students should be careful not to confuse the two words.

Breeding the Donor Cow (continued) If using artificial insemination, the donor cow should be bred at least twice to ensure that all eggs are fertilized.

The Flush Once the donor cow has been bred, the embryos are allowed to grow for six days. During this time the embryos also travels down the reproductive tract from the oviduct (the site of fertilization) to the uterus where they can be flushed out. On the seventh day, the embryos are ready to be removed. This process is called flushing.

The Flush (continued) Embryo professionals use a non-surgical method to remove the embryos. The process requires experience and a patient, steady hand.

The Flush (continued) An injection of lidocaine is given prior to the flush to reduce pressure and stress on the donor cow and to make the flush easier for the ET professional. This is an intramuscular injection given in the fatty part of the tail-head. The effects of lidocaine are seen a few minutes after the injection. When the tail is limp, you can begin the flush.

The Flush (continued) To begin the flush, a catheter is passed through the cervix into one uterine horn. At this point, the ET professional inserts one hand into the rectum and finds the reproductive tract. Holding the cervix in hand, he or she inserts the catheter into the vagina, passing it through the cervix and into one uterine horn. A metal rod inside the catheter steadies the catheter while it is being inserted.

The Flush (continued) The catheter contains a balloon that is inflated with a saline solution in order to seal the entrance to the uterus so fluid and embryos are not lost. Once the catheter is in place, the balloon is inflated by pumping saline through a syringe into the balloon.

Removing the Embryos The uterine horn is filled with flush media and massaged to allow the embryos to flow out of the tract. This process is repeated several times in each uterine horn.

Collecting the Embryos Embryos are carried out of the reproductive tract through plastic tubes and collected in a filter with the flush media. The pores in the filter are smaller than the embryos so excess fluid drains out of the filter without losing the embryos.

Injecting Penicillin After the embryos have been flushed out, uterus injected with penicillin to kill any missed embryos or infections. The donor cow is exposed to infection during the flush due to all the foreign objects that are put into her reproductive tract. Penicillin will kill all infections the donor cow is exposed to as well as any embryos that were not flushed out. We do not want the donor cow to carry a calf because this defeats the purpose of ET.

Embryo Statistics An average of 7-10 embryos is collected from each flush. However, the number of embryos obtained from a single flush may range anywhere from 0-60. Make sure that students know that if an extremely large number of embryos are collected, there is a chance that they may not all be fertilized or in the proper condition for transfer. Careful examination under a microscope will determine this.

Separating the Embryos In the lab, embryos are separated from the flush media and examined under a microscope to determine their quality and stage of development.

Embryo Size and Quality Embryos are microscopic in size (about 0.2 mm). Only undamaged embryos at proper maturity should be transferred.

Embryo Quality The embryos on the left are damaged and should not be transferred. The embryo on the right is of proper maturity and quality and should be transferred.

Transferring the Embryos The embryo to be transferred is put into a small, plastic straw and then loaded into an embryo transfer gun.

Transferring the Embryos (continued) The embryo is then inserted into either the left or right uterine horn depending on which ovary has a corpus lutuem (CL). The CL is a structure on the ovary that secretes the hormone progesterone which is needed to maintain the pregnancy. The transfer begins the same way that the flush does. One hand is inserted into the rectum and locates the reproductive tract and cervix. The transfer rod is inserted through the vagina, cervix, and into the uterine horn that has the CL. The recipient cow’s ovaries are palpated before the transfer to determine which ovary has a CL.

Transfer Immediately or Freeze Embryos should be transferred as soon as possible after the flush (within 8 hours at least). Embryos can also be frozen for later implantation and stored in liquid nitrogen tanks.

Summary ET can be costly, so the return on the investment should always be greater than the input costs. ET should only be performed using donor cows of superior genetics. Bull selection should be based on superior genetics as well.

Conclusion If the required conditions are met, embryo transfer can be a beneficial way to produce superior cattle.

CLICK HERE FOR EMBRYO TRANSFER TEST QUESTIONS

Name __________________________________      1.) Which of the following is a benefit of ET? A. ET is inexpensive and easy to perform B. ET can be done using any cow on the farm C. ET preserves superior genetics for future generations D. ET is an easy way to have twin calves 2.) If embryos are not transferred they must be   A. Refrigerated immediately B. Thrown away C. Stored in excess flush media D. Frozen in liquid nitrogen 3.) An embryo is  A. a fertilized egg B. an unfertilized egg C. an immature egg D. an organism in the last stage of development 4.) Which of the following is used to synchronize estrous cycles of the donor and recipient cow? A. Lidocaine B. Lutalyse C. FSH D. Estrogen 5.) A follicle releases  A. 2 eggs B. 1 egg C. 0 eggs D. 4 eggs 6.) Why is it important to synchronize the estrous cycles of the donor and recipient cow ? A. to make the transfer easier on the ET professional B. so the milk production of the recipient cow will be adequate C. so the reproductive environments of the donor and recipient cow are the same D. none of these are correct

7.) Superovulation causes A. the donor cow to come into heat sooner B. the recipient cow to stay in heat longer C. ovulation to occur earlier D. the ovary to produce many follicles 8.) The donor cow should be bred at least how many times prior to the flush when using artificial insemination?   A. 1 B. 2 C. 3 D. 4   9.) Which of the following determines which of the recipient cow’s uterine horn the embryo will be placed in?  A. the presence of a corpus luteum B. the size of the uterine horn C. the structure of the uterine horn D. the preference of the ET professional 10.) What is the antibiotic used to kill any missed embryos or infection after the flush?   A. progesterone B. prostaglandin C. penicillin D. lidocaine 11.) During a flush, the purpose of inflating the balloon is to A. expand the uterus B. seal the entrance to the uterus so fluid and embryos aren't lost C. stop uterine contractions D. keep the catheter from slipping out 12.) Embryo are approximately ______ in size.   A. 1 mm B. 1 in. C. 0.5 in. D. 0.2 mm

13.) The corpus luteum (CL) is a structure on the ovary that secretes the hormone ____________ which is needed to maintain pregnancy.  A. progesterone B. estrogen C. testosterone D. FSH   14.) The goal of ET is to   A. obtain one genetically superior embryo B. obtain as many embryo as possible regardless of their quality C. obtain the maximum number of genetically superior embryos in a minimum amount of time D. none of the above are correct     15.) The total cost of embryo transfer is approximately  A. $ 500 per flush and $ 400 per calf born B. $ 150 per flush and $ 150 per calf born C. $ 500 per flush and $ 100 per calf born D. $ 300 per flush and $ 270 per calf born True / False T F 16.) ET involves the removal of an embryo from a genetically superior cow and placing t into a cow of average genetics. T F 17.) Donor cows must possess excellent genetics. T F 18.) Prostaglandin (Lutalyse) is the hormone used to superovulate a donor cow. T F 19.) When you observe a cow riding another cow you can conclude that she is in estrus. T F 20.) The only purpose for waiting 6 days before flushing embryos is to allow growth and development. T F 21.) The most important characteristic that a recipient cow must possess is milking ability. T F 22.) ET professionals use a surgical method to remove embryos. T F 23.) An average of 7-10 embryos are collected from each flush.

T F 24.) Embryos must be undamaged and at proper maturity before transferred.   T F 25.) The uterine horns are flushed only once to allow embryos to flow out of the tract. T F 26.) Filters are designed to keep only the good embryos and let the bad ones drain off with the excess fluid. T F 27.) Embryos must be examined under a microscope to determine their quality and stage of development. T F 28.) The embryo transfer procedure has a fairly low difficulty level. T F 29.) Recipient cows do not contribute any genetic material to transferred embryos. T F 30.) The donor cow can either be bred naturally or by artificial insemination.