Creating a life from a transferred embryo of no more than 150 cells is a miracle every time a new calf or lamb is born. The first calf resulting from an embryo transfer was produced experimentally in 1951, but it took more than 20 years to commercialize the science.
NOW:
A major breakthrough occurred when calf embryos could be frozen and used later.
“At this point, there is no expiry date,” said veterinarian Roger Davis of Davis-Rairdon International at Crossfield, Alta.
Davis, who works exclusively with cattle, and Ilena Wenger and Lynn Tait of the small ruminant practice OC Flock Management at Bowden, Alta., are among the few veterinarians in Canada to focus on artificial breeding using embryo collection and transfer. OC Flock Management also collects semen from sheep and goats.
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Davis was among the early adopters of the technology, which had picked up traction with the introduction of Continental cattle from Europe. Exporting a tank of frozen embryos encased in liquid nitrogen was cheaper and safer than shipping live animals from France to Canada.
He has been transferring embryos since 1980.
In the early days, embryo collection involved surgery and general anesthetic. It was invasive, and the cow was likely infertile after two sessions because of scar tissue forming in the reproductive area.
Non-surgical methods were developed in the late 1970s, allowing numerous collections from elite females.
Until freezing was perfected, embryos were transferred fresh from the donor cow to recipients that had received hormone treatments to bring them into estrus at the same time.
There were days when they collected from three donors and had no viable eggs to pass on, and consequently, no pregnancies. Other times, they might collect 50 embryos and would not have enough recipients, so the eggs were thrown away.
The technology to successfully freeze embryos was introduced in 1975, but it took a few years to train veterinarians and make it commercially viable. It was still far from perfect.
“At that time, we would discard about 30 percent of the embryos we froze after we thawed them,” Davis said.
“If we achieved a 40 to 50 percent pregnancy rate, we were quite excited.
“The advent of freezing was probably the biggest breakthrough in embryo transfer because now it could be more efficiently done,” he said.
“You could set up recipients or you could collect embryos and freeze them and have a bank of embryos as back-up plans to transfer in case you did not get enough fresh embryos.”
Freezing and thawing techniques have improved significantly, which makes it easier to work in the field where conditions are less than ideal.
The adoption of ultrasound also allowed veterinarians to check implanted females at 28 to 30 days. They can also do a manual palpation to confirm a pregnancy at around 40 days.
The cattle can be synchronized again if there is no pregnancy and another attempt made.
One bovine embryo is typically implanted. Veterinarians do not want male and female twins because the female is likely to be a freemartin, which is infertile. The male hormones develop sooner in freemartins and suppress the development of the female reproductive system.
Improved synchronization has also simplified super ovulation of the donors so that more eggs are released and ready for fertilization, usually by artificial insemination. The embryos are collected from a cow’s uterus at around seven days of pregnancy and contain about 150 cells.
The average yield is now seven or eight freezable quality embryos, which are referred to as grade one embryos.
Those that do not freeze as well can be transferred fresh, so a veterinarian may capture 10 for every cow that is super ovulated.
The technology has upgraded cattle around the world.
Research has proven there is no disease risk when embryos are properly washed in a special enzyme solution. Each is protected by a shell called the zona pellucida. This shell cannot be cracked or penetrated if embryos are being exported.
“Many countries around the world accept washed embryos, providing that shell around the embryo has not been violated,” Davis said.
The embryo transfer industry is highly regulated.
The Canadian Embryo Transfer Association (CETA) governs practitioners with an intense certification program that demands regular upgrades to maintain high standards of work.
“It was the first certification program in the world, and a lot of vets from other countries use ours as a template,” Davis said.
Almost all the work done at OC Flock Management is exported. There are multiple layers of oversight and regulation because the veterinarians perform surgery, offer quarantine areas and export embryos.
The current facility was built in 2003 with certification from the Canadian Food Inspection Agency, CETA and the Alberta Veterinary Medical Association. It is also the only Canadian unit to receive certification to export sheep and goat embryos to the European Union.
The clinic is among the few that works with sheep and goats, and veterinarians regularly travel to collect and implant embryos. They also train international veterinarians and students from the University of Calgary’s veterinary faculty.
The work is different from what’s done at bovine clinics because sheep and goat reproductive systems are different.
“You superovulate the same way, but collection is very different,” said Wenger.
“Everything we do in sheep centres around the fact that we can’t get through the cervix and deal with reproductive technologies in the same way as cattle.”
The clinic, which started in 1996, collects semen and performs laparoscopic embryo collection.
Sheep and goats respond to light so their breeding time is seasonal and work is hectic from August to February, when the animals are responsive.
The work is painstaking and relies on good technique to ensure successful pregnancies.
The females go under general anesthetic, their lower bellies are shaved and they receive a small incision to reach the uterus. The incision is made in a different place with each collection.
The entire procedure takes about half an hour. The females can be rebred and deliver lambs successfully.
“We will flush three times in a season, and you can flush a total of five or six times in the lifetime of a sheep before you see issues, and that is with an experienced surgical team and with very good surgical technique,” Wenger said.
The number of embryos varies, but prolific breeds can yield up to 10 to 12 embryos while others produce six to eight.
Pregnancy rates are comparable to cattle. Fresh embryos can result in a successful pregnancy 70 percent of the time while frozen embryos catch up 50 percent of the time.
Veterinarians put two embryos in recipients because sheep and goats generally have twins.
“You need to be very particular on your recipient selection,” she said.
“Recipients are usually selected for their maternal abilities. They’ll have good milk, they’ll be experienced so you know they will raise a lamb well.”
Conception also depends on the animal, the environment, when the embryos were collected and if the animals were under stress.
The sheep are left alone for 30 days to see if conception is successful.
Goats are also collected via surgery, although some new work on cervical flushes has been conducted.
“I haven’t seen the research yet to show we get as good a recovery rate,” she said.
Embryo freezing is handled in the same way as cattle. However, only one bovine embryo is placed in a straw while one to four sheep embryos may be inserted.
Canadian livestock genetics are valued around the world because the animals are vigorous and healthy. International clients are also looking for the country’s considerable genetic diversity, including sheep breeds that aren’t found elsewhere.
THEN: Guelph scientists develop embryo freezing technique
Two Guelph scientists have developed embryo freezing techniques which may contribute to a breakthrough in female livestock reproductive capacity.
According to a report in the University of Guelph News Bulletin, Prof. J.W. Macpherson and Dr. Paul Fiser of the university’s department of animal and poultry science have been working on mice embryos to develop the technique.
Dr. Fiser has developed a technique of freezing the embryos after they have been surgically removed from the donor animal and reculturing them with about an 80 percent survival rate. The donor animals are injected with hormones to make them produce many times the normal number of ova.
The embryos are placed in a solution which protects them and at the same time dehydrates them as the temperature is lowered to minus 198 degrees Celcius. Success depends on the composition of the solution and the rate of freezing.
When the embryos are thawed and recultured they start to grow normally and can be implanted in a host animal where they will become normal fetuses.
Pilot studies have been so successful that the two scientists will begin research on bovine embryos next.
