Embryo transfer (ET) is an invasive procedure performed by a licensed and trained veterinarian that is becoming is widely used in the meat goat industry by the showman, hobbyist, and commercial producer. Like laparoscopic AI, this technique is fairly cost prohibitive due to its commonly practiced methods involving surgical collection and transfer of embryos. Although success rates are increasing as techniques are mastered and practitioners gain experience and knowledge, ET programs have many limitations. Still, more and more producers are finding that a well-planned ET program involving the use of a knowledgeable and well-experienced technician who offers careful attention to detail with regard to sterility, synchronization, superovulation, and the appropriate selection of both donor and recipient does, can often achieve an acceptable rate of recovery and transfer of high-quality embryos.
Embryo transfer can be performed successfully both in and out of the normal breeding season. However, it is best performed when the does are actively cycling and exhibiting normal behavioral estrus. Furthermore, the most successful results occur when the participants are two to five years of age (the prime of their reproductive years), are in good health, and have a body condition score of 3 to 3.5. By observing all of these conditions, an ET program can offer the highest rate of success for both the ET technician and the producer.
A major deterrent to some producers is the requirement for many recipient does. A suitable recipient doe is one who has proven her reproductive abilities. Such abilities include not only trouble-free kidding, but natural mothering characteristics and an adequate milk supply for rearing kids. Once recipient candidates are selected, they should be separately housed and managed for several weeks prior to and after their scheduled transfers. Careful attention to management must be paid to the recipient herd insuring that high levels of nutrition, excellent health, and a low stress environment are maintained for successful implantation and pregnancy rates.
Prior to transfer, each of the recipient does must be synchronized to be at the same stage of their estrous cycle as the donor doe. Does can be synchronized using a variety of methods; the most common choice of most ET technicians being progestagen therapies of one sort or another.
Superovulation methods
Donor does are predominantly does of high value to the herdsman. These does have genetic potential, or proof of such, which warrants the cost and inconvenience of the flushing procedure. Traditional protocol for the donor doe involves a menu of hormonal treatments directed at the superovulation of her ovaries. Follicular stimulation is accomplished by way of the doe’s FSH and LH levels, and is of primary importance in achieving a satisfactory superovulation response. Superovulation is commonly induced through administration of decreasing doses of follicle stimulating hormone (FSH), 1 to 5 mg, injected in 12-hour intervals over a period of 3-5 days around the time of termination of the progestagen treatment. Improvements in the consistency and predictability of the superovulatory response have been achieved through corresponding protocols involving prostaglandin (PG) and luteinizing hormone (LH) treatments.
Other methods of superovulation utilize either an FSH product alone or in combination with PMSG (eCG). Some practicioners have concluded that FSH offers superior results when compared with PMSG protocols, in that PMSG can cause overstimulation of the ovaries causing the release of larger numbers of oocytes. These greater numbers can result in higher ratios of unfertilized oocytes and lesser quality embryos. This may be attributed to insufficient numbers of spermatozoa for adequate numbers of “accessory sperm,” especially when AI is employed as the means of fertilization. Bucks who are exposed to more than one or two superovulated does may also fail to have adequate numbers of spermatozoa to properly fertilize the large numbers of oocytes.
It is recommended that insemination of the donor doe be performed 12-24 hours following the beginning of behavioral estrus by either natural service or, although not always as successful, via cervical or trans-cervical AI with the use of 300 million live, motile spermatozoa as would be expected to be found in five 0.5cc straws. To increase the overall success of artificial methods of fertilization, the doe should be monitored to determine the proper time of servicing. These recommendations are based on ensuring that sufficient numbers of “accessory sperm” are present for the successful fertilization of multiple ova resulting in high grade, viable embryos.
Use of laparoscopic/intra-uterine AI is usually not performed in this procedure in an effort to avoid additional manipulation of the uterus and oviducts. However, when performed 24-hours following first evidence of estrus in the donor doe, laparoscopic AI has been reported to offer some success.
Acceptable resulting ovulation rates from the methods described range from 10 to 25 ova produced, but the number of viable embryos for ET use may be significantly lower.
Embryo flushing
Harvesting of the donor doe’s resulting embryos (fertilized ova) traditionally involves a licensed veterinarian and is performed 5-6 days following applied fertilization methods. The donor doe is denied food or water for 24-36 hours before surgery as she will be anesthetized during the procedure. Her abdominal area is clipped and prepared for aseptic surgery. Once under anesthesia, a midventral or flank laparotomy protocol is used to expose the uterus and the ovaries are examined to determine the response to the superovulation therapy. When a positive determination is made, the uterine wall is penetrated and a catheter is inserted into the uterine horn. A flushing media is infused through the catheter which facilitates the flushing of the embryos into a Petri, culture, or collection dish. Once completed, the same procedure is followed to flush the opposite uterine horn. The puncture sites are then left unsutured.
The disadvantage of such an invasive procedure on repeated occasions is the likelihood of resulting adhesions that may interfere in subsequent collections. Recently, newly practiced techniques involving laparoscopy to accomplish the same goal have met with good success in goats. However, this technique is more difficult and requires a technician who is well practiced in such a procedure.
Vaginal flushing/trans-cervical embryo collection methods are in their infancy with regard to goats. Nevertheless, there are many published reports of successful nonsurgical collections. This practice is on the horizon for the producer and should be considered as it offers a lower chance of postsurgical adhesions and allows for a much greater number of collections over the doe’s lifetime. Flushing by this method is performed similarly to the techniques of trans-cervical AI in sheep. A duck billed speculum is used to see the external os of the cervix and grasp it with forceps. The speculum is removed and the os is carefully brought to almost reach the vulvar opening. A catheter is passed through the cervix and positioned to flush either the right or left uterine horn. Multiple flushings of each horn are performed along with massaging techniques. Reported results are mixed as many technicians feel that the entire uterus is not always able to be flushed. Harvested embryos differ considerably in number according to the flushing method used. It has been reported that in vaginal flushing often no embryos are harvested whereas three to four can be expected. Still other findings report that embryo recovery can be comparable to collections by surgical means.
Once collected, the flushing medium is searched for its expected number (based on the doe’s number of corpa lutea) of ova. Once recovered, ova are scrupulously examined for quality and very distinct handling procedures should be practiced to reduce the risk of disease transmission. The ova are then washed and examined to assess the number that have cleaved (fertilized), and their stage of development. Once this is determined, each ovum is drawn into the tip of a small-bore catheter attached to a small syringe and either transferred to the recipient doe or processed for freezing.
For the purpose of cryogenically freezing and storing embryos, only those of the highest quality and grade should be processed. Limited progress has been made in the cryopreservation of goat embryos and success is highly related to the type of cryoprotectant used. Pregnancy rates from the transfer of frozen embryos are substantially less than rates obtained with freshly harvested embryos.
Embryo transfer
The practice of transferring harvested embryos to recipient does is again an invasive technique, surgically performed. Potential recipient does are anesthetized, their abdominal area is clipped and aseptically prepared for surgery. A small, midline incision is made and the ovaries are examined for corpa lutea. If determined to be at a stage suitable to that of the embryo, the embryo is either transferred into the oviduct via a catheter or placed directly into the uterine horn by way of a needle, depending on the stage of the embryo’s development.
When the transfer is “laparoscope-assisted” or a “laparoscopic method of transfer” is utilized, the doe is similarly prepared for the surgical method described above except the recipient doe is positioned and two cannulas are used as would be done for laparoscopic AI. The ovaries are examined by way of the laparoscope and a determination is made as to the condition of the corpus luteum. If a positive determination is made, in a “laparoscope-assisted” method the tip of the uterus is punctured and the embryos are transferred as in a surgical method. Once transfer is complete, the technician sutures the small incision. A “laparoscopic method of transfer” requires the embryos be loaded in a 0.25 or 0.5 cc straw that is inserted into an AI gun fitted with an injection tip. Protocol similar to that of laparoscopic/intra-uterine AI is followed for the deposit of the embryo.
In the fresh transfer of embryos to synchronized recipient does, although lesser quality and grade embryos can be used, only #1 grade embryos are recommended for a high success rate and outcome. In some cases where donor does have produced a limited number of #1 grade embryos, recipient does with multiple corpa lutea may be given a matching number of embryos involving the transfer of one #1 grade embryo and additional #2 or lesser grade embryos, in hopes that one or more of these sub-standard embryos might survive. The use of sub-standard embryos in combination with the #1 grade embryo(s) appears to have no negative influence on the latter, although there is also no additional guarantee of success. The recipient doe’s stage of ovulation being as similar as possible to the donor doe’s is believed to have the greatest influence on the success of the procedure. By way of any method, the donor doe’s embryos are placed in the recipient doe on the side that has a corpus luteum present. The number of corpa lutea on the ovary determines the number of embryos the recipient doe may receive.
Immediately following the procedure, all does are brought through recovery in a carefully controlled, low stress environment with great attention paid to their management and daily conditions for several weeks.
A list of some companies offering embryo transfer services is located at the end of the module.
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