Until recently, collecting pig embryos and implanting them in sows without surgery could not be done. But a new embryo transplant method, developed by the Wageningen Agricultural University (WAU), in the Netherlands, no longer requires surgery.
And, like artificial insemination (AI), embryo transplantation for pigs can now be carried out on the farm.
"Our new method of embryo transplantation has resulted in such a large number of pregnant animals, that it is now ready to collect experiences on farms," says Wouter Hazeleger, researcher of the Department of Animal Husbandry at WAU. An international patent has been applied for.
Before this breakthrough, collecting and implanting pig embryos requiring surgery only saw limited use in pigs.
Catheter Simplifies The Procedure The new method of implanting the embryos in sows resembles AI. A specially developed catheter consisting of a thin, flexible, bent rod and a thin tube is used for the embryo transplant procedure.
The end of the rod and the tube is inserted through the cervix into the central body of the uterus. With a tenth of a milliliter (3 fl. oz.) of liquid substance, the embryos are subsequently transferred into the uterus. The embryos move about and nestle into the uterine horns.
Simple As AI At the age of five days (5-6 days after fertilization), the embryos are placed into the recipient sows. This is approximately five days after the sow is in estrus.
Despite the fact that the sows no longer show a standing reflex, they stay perfectly calm when the embryos are inserted. A feeding cubicle with ample working space and some feed to distract the recipient sow are sufficient to insert the embryos smoothly into the uterus. The insertion takes about as long as AI does.
Hazeleger explains, "Inserting the embryo via a catheter requires just as little effort as inserting a pipette for artificial insemination. It only requires some extra hygiene. If you see to it that the sow has sufficient fodder during the treatment, she just keeps on eating."
Perfecting The Procedure A few years ago, using the WAU method of non-surgical embryo transplantation, about one third of the treated animals became pregnant. The average litter size was approximately 6.5 piglets. This low figure was, amongst other things, caused by damage to the embryos.
Since then the method has been perfected with the private financial support of the product boards for Livestock, Meat and Eggs, Dutch Society of Pig AI Organizations, Euribrid, Dutch Pig Herdbook Society, Dalland and Dumeco breeding companies.
Currently, about 60% of the recipient sows become pregnant and, when checked a month after transplantation, about 11 well-developed fetuses are commonly present. From this a litter of at least nine piglets can be expected.
"The results of the non-surgical method are, on average, even better than the transplantation carried out with surgery," Hazeleger says.
During the research in Wageningen, photographs were taken of all the transplanted embryos that were used to classify the development of the embryos. This research verified that the success rate could have been improved to over 75% if only the better-developed embryos had been identified and transplanted. "A careful selection of embryos is important. It clearly enlarges the chance of pregnancy," Hazeleger observes.
Synchronizing Sows Recipient sows, in which the embryos are to be implanted, are not inseminated. However, for embryo transplantation to be successful, it is necessary for the recipient sow to be in the same stage of the estrous cycle as the donor sow. The development of the embryo to be transplanted must be attuned to the development of the uterus of the sow in which it is placed. Therefore, to synchronize the donor sow and the recipient sow, it is necessary to synchronize heat and ovulation artificially. This avoids the possibility of implanting an embryo of the wrong age and in the wrong stage of development.
Artificial synchronization is a time-consuming process and does not always give the desired results in all sows. But again, for embryo transplants to be successful, donor and recipient sows must be synchronized as closely as possible.
Another possibility is using ultrasound scanning to determine the moment of ovulation. In this way the stage of the uterus and the embryos could be carefully determined and recipient sows could be matched to embryos of a certain age.
Collecting Embryos The embryos that have been collected up until now were obtained through slaughter. Hazeleger believes large numbers of embryos could be obtained from inseminated sows and gilts destined for slaughter, thereby serving as an important embryo source in the future.
In time, it will be possible to collect ripe egg cells from sows or gilts, fertilize them in a laboratory, and grow them into embryos. Some day, it may even be possible to collect unripe egg cells, allow them to ripen in a laboratory (in vitro maturation) and subsequently to fertilize them.
"Many of the technical possibilities which are now available for human beings and for cattle will, in time, also be available for pigs. But they still need some further improvement," Hazeleger explains.
Shortening The Uterine Horn As noted earlier, surgical methods for transplanting pig embryos are not new. But, these methods are little used because they are not suitable for practical application on a large scale.
Because the uterus of a pig consists of one central uterus body and two large curled horns, it is difficult to flush the embryos out. This made obtaining embryos from live sows impossible.
But a few years ago, Hazeleger and his WAU colleagues developed a procedure that made continuous operating on donor sows unnecessary. Now only one operation is required to shorten the uterine horns of the donor sow to a length of 8 in. (20 cm.). The connection with the ovaries remains intact.
After insemination/fertilization, embryos can develop normally, the same as before the uterus was shortened. Shortening makes it possible to collect the embryos via the natural birth canal by using a catheter.
Flushing The Embryos The WAU researchers found a reasonably simple solution for inserting the flushing catheter. A long thin rod with a bent head is inserted into the heavily pleated cervix via the vagina. By turning the rod to the left and right, the bent head is maneuvered between the pleats of the cervix and into a uterine horn.
Then, a second thin rod with a double tube is pushed into the uterus through the straight passage that has now been formed. The two tubes make it possible to flush the uterus and to collect the flushing fluid containing the embryos.
Hazeleger explains, "After one operation a sow can deliver embryos for years." However, he still finds the method to harvest embryos somewhat lengthy for large scale, embryo transplant application. Hazeleger predicts the process will only be used for obtaining embryos from animals at the top of the breeding pyramid.
Additional Work Required Pig farms are currently being sought in the Netherlands to apply the non-surgical embryo transplantation methods. The findings from this work will provide information about the optimum holding temperature and maximum keeping times of embryos.
Freezing pig embryos for long-term preservation is not yet possible. Hazeleger does not expect this to restrain the introduction of embryo transplantation, however. "If there are sufficient embryos available, freezing is not necessary. Pig sperm is also used on a large scale and isn't frozen either," he points out.
Ordering Embryos The scenario for the future is that pig farmers will be able to order embryos with a particular genetic background from embryo transplant stations. In the beginning, it will still be necessary to attune supply and demand. Dates and embryos availability will have to be reserved in advance. These dates can then be used to coordinate the weaning dates of donor and recipient sows to ensure estrous cycles and ovulation are synchronized.
For practical application on the farm, five days after ovulation (about six days after the start of the in-heat period) the transplanter would insert the embryos into the recipient sow. If the recipient sows cycle very early or late, the producer still has the option to artificially inseminate those sows.
In the future, Hazeleger believes it will be possible to order frozen embryos from a laboratory that are in a certain stage of development, matched to the recipient sow.
Other Advantages Non-surgical embryo transplantation also offers the advantage of reducing the risk of introducing diseases, particularly compared to live animal introductions.
The embryos, in their transplantation stage, are still surrounded by an egg fleece, thus protecting it against germs, researchers explain. In addition, the embryos are washed several times after collection, sometimes in combination with an antibiotic or disinfectant. This reduces the risk of contamination by embryo transplantation to virtually nil.
And, there are genetic improvement advantages, such as buying new genetic material that can be purchased via embryos and implanted in all sows in the herd. In this way, transfer of new genetic material can even be improved and closed breeding and production herds can be developed and maintained.
Exporting embryos could save a lot of money when compared to the export of live animals, especially when a quarantine period must be administered. Likewise, transporting embryos is much cheaper than transporting live animals. Of course, the ability to store pig embryos for any length of time remains a limitation.
The embryo transplant process opens up possibilities for more supply locations, even abroad, and offers a wider choice of genetic lines. "Embryo transplan tation enlarges the freedom of choice on breeding farms," Hazeleger adds.