Embry Transfer is increasingly being used for various reasons. These include
With such a limited amount of Gypsy Horses in Australia ET is an attractive procedure for getting quicker returns from your investment or to simply increase the breeding population available in Australia. However done irresponsibly it will further reduce our gene pool rather than help the breed. There are also some farms in the US now that seem to be producing "litters" of embryo foals for the quick dollar rather than making a few superior embryo foals available.
There is no doubt ET is a very useful tool and I am certainly not against it. However I would like to see some controls put in place to combat what is often called Embryo Abuse.
I honestly can't remember where I got this
article, off the net somewhere. But it is a good article explaining ET, problems and otherwise. I've added a bit about super ovulating mares below
it, plus a short article on Cloning. Proof of the strange new
world we live in.
The American Sporthorse was one of
the first organizations to promote ET in horses, in the early 1980’s.
Their research money helped make Colorado State University (where much of
the early work was done) one of the foremost facilities for equine
Some breed registries have
restrictions about how many foals can be registered per year from the same
donor mare, while others accept unlimited registrations. The AQHA, for
instance, only allowed one foal per mare to be registered annually but
recently relaxed this rule, due to pressure from members. Now that more of
the foals can be registred with AQHA, this has opened more doors from a
research standpoint. Even for the breeder that doesn’t use ET, we can all
benefit indirectly from what we learn (about equine reproduction) by doing
History of equine ET -The person
doing embryo transfers the longest in the United States is Stephen
Vogelsang, now doing reproductive work at Wichita Ranch at Brenham, Texas,
where he has worked for 11 years. He became interested in embryo transfer
while in graduate school at Texas A&M, and did the first equine embryo
transfer in 1977. “I had been exposed to ET work in cattle, and didn’t see
why we couldn’t do this in horses. I worked with Dr. Duane Kraemer, a
professor at Texas A&M who was a pioneer in ET work. He had just
finished doing the first ET in primates. We didn’t see any reason we
couldn’t do it in horses--if we could get the research animals together,
which I was able to do," says Vogelsang.
“I got an embryo out of the first
mare we did, and that first transfer resulted in the first ET pregnancy in
horses in the U.S. in 1977. This had been done already in England and
Japan, so that made ours the third one in the world. At that time, people
felt ET would not be accepted by the horse industry--that it would be a
technique just used for research,” he says.
“The first ET foal (“Miss T”) we
produced at Texas A&M in 1978, we submitted for registration in the
AQHA, and they would not accept it because there was another foal born
that same year from the donor mare. But AQHA set up guidelines for ET, and
decided to accept this technique on a limited basis. At that point, they
only let us do it in mares over 15 years-old or barren for 3 or more
consecutive years. We functioned under those requirements until 1988 when
the rules were changed to allow ET on any mare,” he says.
“After I finished at Texas A&M,
I worked for Quarter Horse breeder Jack Benson, from 1978 to 1980, at
Stallions Unlimited in Brenham, Texas. We stood The Investor. Then I went
to work for Sam Wilson in Pattison, Texas who stood Skip A Star and Son of
a Doc, and a few lesser known Quarter Horse stallions. While I was there
(1981-1983), I bred 500 to 600 mares a year.” In 1984, he went to work at
Granada Equine Service, and was with that company for 10 years.
“Granada was, at that point, the
largest company involved with ET in cattle in this country. At one time
they were doing 10,000 ET pregnancies a year in cows. With the technical
support I had there, we started doing commercial ET in horses,” says
Why Use ET? - Embryo transfer is a
way to get foals from a problem mare that cannot carry a pregnancy, or to
extend the reproductive life of an older mare, a way to raise foals from a
mare while she continues a performance career, and a way to “back up” a
mare that foals late in the season, without losing a year of reproduction.
Some breeders use ET to get more than one foal a year from a
It’s also good insurance. There have
been cases in which a young mare dies during her showing career, yet she
had an embryo being carried by a recipient mare, and thus had one more
foal after she died. Use of ET allows mares to have a double career; they
don’t have to take time out to have a foal.
“Probably the main reasons people do it is
so they can keep showing the mare, or to get foals from her by multiple
stallions,” says Vogelsang. “People book mares to more than one stallion,
and breeding contracts today address this issue, as to which stallion the
mare will be bred to first, at what stage she will be bred to the second
stallion, etc. For instance, in our contract for Mecom Blue, it states
that he’s the first stallion that the embryo is produced by, and the mare
won’t be changed to another stallion until we actually develop a viable
pregnancy. Otherwise, you get into a situation where you have multiple
stallions involved and if there’s a hang-up along the way, then you have
ET is a good tool to find out what
stallion a mare crosses best with. You can get some foals on the ground
and get them trained, rather than having to wait until she retires from a
performance career to finally figure it out. You may know her best cross
by the time she’s 7 or 8, and can raise quite a few more, if the stallion
is still alive.
Vogelsang says, “Due to AQHA
restrictions, we started, at first, just doing problem mares and old
mares. We thought it would be a panacea for the problem mare. We
subsequently found out that a lot of those mares, because of their age or
inherent problems, still had a low success rate with ET.”
He thinks this is due to the fact
that an embryo from the old mare has less quality than embryos from young
mares. “The old mare has a low reproductive success rate because of other
factors besides an old uterus with senile changes and scarring. Even
though you take her embryo and put it into a young, healthy uterus, you
may not always be successful. The embryo from the old mare is just not as
viable as that from a younger mare,” he explains.
“In looking at comparisons with
other species, you find that in the older human female, such as a woman
over 40, there are some genetic problems you are more concerned about than
in the younger woman. There’s a lot more risk, and it’s not just the
uterus, but also with the oocyte itself. Remember that all those eggs are
what she was born with--the eggs she has throughout her life. The female
is not reproducing eggs like a male is reproducing sperm; all her eggs
have been there from the beginning,” he says.
“If you take a mare that’s 20
years-old or so, those eggs you are dealing with are 20 years-old. When
you look at the pregnancy rate with old mares, you’ll end up with--even
with good management--about a 10 to 15 percent lower success rate,
compared with normal, healthy young mares,” he explains.
He started downplaying ET work for
problem mares and putting more emphasis on using young mares that are
still performing and at the peak of athletic careers--at the height of
their popularity. “It made more financial sense to work with that young
mare, just as a stallion is most used when he’s young, popular and
winning. We needed to take the same attitude toward mares, since at this
point in their lives and careers their foals are worth the most. They will
be more in demand when the mare is winning than they will when she’s older
and out of the limelight. You can get some ET foals from her while she
continues to perform,” he says.
“This idea started catching on in
the mid-1980s, once we broke down that barrier of people thinking that an
ET foal might be inferior to a natural foal because it didn’t have its own
mother raising it--especially after ET foals started winning at cutting.
Then it almost became faddish, with cutting horses, to go that direction.
It makes a lot of sense with the young mare; if she’s able to win $20,000
or more a year she can more than justify doing ET and producing a foal
that will be in demand when she’s at the height of her popularity. Doing
ET with young mares has now surpassed use of ET in problem mares and older
mares as the number one reason why we do it,” he says.
“Another reason (to use ET) is with
an old or debilitated mare that has a physical problem such as founder or
a torn cervix or anything that prevents her from carrying a pregnancy to
term. A fourth reason would be to move a mare earlier in the season if
she's foaling late. You can leave her open and breed her earlier the next
year, and yet not miss a year of production, since a recipient mare can
carry a foal for her.” Now a fast-growing reason for using ET is to
produce more than one foal a year from a certain mare.
Costs of ET Services - The cost of
doing ET is anywhere from $2000 to $5000, and this includes the recipient
mare as part of the package. “A lot of people will charge a $1000 deposit,
which includes a number of embryo collections. I charge a $300 collection
fee for each embryo collection. That way if somebody does one collection
or two collections and we’ve not had any success and they want to quit at
that point, they still have that option. We also emphasize that the $2000
to $5000 for the ET does not include the stud fee for the stallion used;
it’s just for the ET service,” he explains.
Costs have come down from what they
were in the beginning. “There are some labs that are doing it cheaper than
others, but you need to do your homework and know exactly what you are
paying for. With the cheaper ones, the mare owner is usually incurring the
risk regarding the recipient mare. If something happens to her, it’s your
responsibility. In other contracts, you have some guarantees involved.
Some facilities have more track record and you may have more chance for
success.” You basically get what you pay for.
Factors That Affect the Success Rate - “The
main factors that affect success with ET are the donor mare herself, the
quality of the recipient mare, the overall quality of the embryo, and
season of the year. The mare herself is the first factor--whether she’s an
old mare with a problem (like chronic founder), and in a lot of pain;
that’s not a positive situation as far as trying to get her pregnant. For
ET work, she has to get pregnant first. Along the same line, if you are
dealing with a 25 year-old mare that hasn’t had a foal for 3 or 4 years,
you’re toward the end of the game with her; you’d have to be very lucky,”
he says. This is why most of the ET work today is concentrated around the
Some of the mares that are hard to
get embryos from are mares that are chronically infected, and old mares
that accumulate a lot of fluid in the uterus. A mare that just has
degenerative changes, with no concurrent infection or fluid buildup, will
furnish embryos though recovery rate will be lower. These are usually
older mares, and there are some other senility changes that go along with
this condition. They may have transport problems (getting a fertilized egg
to the uterus) in the oviduct, or fibrosis (scarring) that interferes with
passage of the egg.
“The next factor that affects
success is the recipient mare,” says Vogelsang. “That’s one reason we use
our own recips (rather than a mare provided by the client) because we have
more history on them. Reproductive health of a recipient mare is very
important. This is probably the most critical thing, regarding the success
of the transfer, because that’s where the embryo is going,” he
The third factor is the quality of
the embryo removed, which in many ways also comes under the first category
(age of the mare). “Regarding age of the embryo, the older it is, the more
risk for failure. We primarily deal with 6 to 7 day embryos. When you get
past day 8, you are dealing with an embryo that’s relatively large and
easy to damage. Age of the embryo will be controlled by how accurate your
detection methods are. This has improved immensely over the years with the
way we utilize ultrasound compared with just palpation,” says Vogelsang.
Time of year can be a factor (you
want it to be at the optimum time, reproductively, for the mares), and
even the stallion is important, regarding the survivability of the embryo.
“In cattle work, there are embryos by certain bulls that have much higher
success rate than those from other bulls, and the same is true with
horses. Some stallions I’ve worked with produce very hardy embryos, while
some others are more fragile,” he explains.
Multiple Ovulations - “A common
question is whether we can get more than one egg at once, like we do in
cattle. In horses, it's been mostly single egg collection until recently.
Most of the super-ovulation products for horses were still experimental
until a few years ago. A lot of people are doing it now, but I want a
little more research data before I start doing it on a large scale. Most
of the mares people want this done with are high dollar mares, so I’ve
been a bit conservative up to this point,” he says.
“There's a tremendous amount of
individual variation on success rate. You’ll have some mares, depending on
how they build follicles, that will respond very positively. When you
stimulate a mare to super-ovulate, you might have 3 or 4 ovulations or, in
extreme cases, maybe 6. In most cases you’ll get 3 ovulations on average.
And there’s a significant percentage of mares in which you won’t get a
response to the drug. The cost will range from about $300 to $400 for the
treatment, and it may not work.”
“You can follow and map those mares
over multiple cycles, and with experience you’ll be able to tell whether a
mare will respond well to the drug--which ones will be a good risk for
this technique and which ones won’t.” You can get to know the mare, to
determine which ones to gamble on and which ones would be a waste of
Double ovulation in the mare occurs
naturally about 10 to 15 percent of the time (twins). Some mares have
double ovulations more consistently than that, and work out very well as
donors because there is no problem transferring both eggs. Many mares
double ovulate, but under natural conditions few twin pregnancies go full
term. Mares have a way of reducing the extra embryo themselves. By the
time most people know a mare is pregnant, there’s usually only one fetus.
“Your possibility of transfer success with a twin is just as good as a
single. I usually have at least one set of twins born per year, carried in
Reducing the Drawbacks of ET - “The
downside of using ET is that it’s a reproductive insult to the donor mare.
We must keep this in mind in terms of how many times we do it with her. At
one point during the early years of ET, we felt flushing a mare’s embryos
had no effect on her future fertility, but it can, if you overdo it. You
must realize that when we do ET collection there’s always the possibility
of contamination and infection. You’re going through a closed cervix (the
mare is out of heat by the time you collect the embryo), so you must
dilate the cervix, possibly causing a small amount of irritation. If you
do it too much, I suspect this could result in adhesions. This problem
with the cervix could also be the result of mares not carrying foals
“In those mares, even if you have a
little damage in the cervix, by letting them go through a normal pregnancy
it seems like the pregnancy restores the normal integrity of that cervix.
When the mare goes through a normal foaling process, it’s a natural way
for the cervix to re-establish itself. Pregnancy shuts the uterus down for
awhile (no continual cycling); the mare goes through 11 months in which
the uterus is closed off from the outside, and this gives it a chance to
restore itself. This is my theory, but it seems to be a factor,” Vogelsang
“I’ve had some mares that you can do
2 embryo collections and you’ll notice they have a lot of inflammation. So
you need to back off, give the mare more time, skip a cycle. Then you can
come back and do it again. You can’t just keep flushing her or you’ll get
to the point where you can’t recover embryos from her at all.”
A technique developed for problem
mares, called GIFT (gamete intrafallopian transfer), involves recovering
the unfertilized egg from a mare’s ovary, putting it into the oviduct of a
recipient mare, then breeding the recipient mare--having it fertilized in
the recipient mare. This is more complicated and expensive than ET, but
can work sometimes to get a foal from a mare with fertilization and
transport problems (getting the fertilized egg from the ovary to the
uterus where it can be collected) or degenerative changes that prevent her
from becoming pregnant.
Recipent mares - Vogelsang says the
main criteria for a recipient mare is that she be reproductively healthy,
with adequate pelvic area; it doesn’t matter what breed or size she is, if
she’s an easy foaler. “There was research done in Europe where they put
embryos from normal size horses into pony mares. Those foals were smaller
at birth from the pony recipient mares, but by the time they were of
weaning age they’d caught up and were no different in size.”
The best recipients are usually
about 5 to 7 years-old. This is the easiest age group to get pregnant.
“They also need good vulva conformation (vertical). If a mare has a sunken
anus, she’s more prone to develop infection. I don’t want a mare that
needs a Caslick’s; I don’t want one that makes more work for me,” he
Recipient mares need not be big.
Some people think a draft mare would be best, but as a general rule draft
mares are not as dependable reproductively. There’s also more feed and
upkeep with a big mare. Many recipients are Quarter Horse or Quarter Horse
type, Thoroughbreds or Appaloosas. Many people doing ET work specify the
need for “roomy” recipient mares, but Vogelsang points out this does not
mean size of the mare, but rather her pelvic area. “I've seen some
Thoroughbred mares that had quite a bit of size, but they were small
through the pelvis. Those kind of mares are not a good choice for
recipients, and you’ll discover this problem when you palpate them. Just
as in cows, pelvic area is more important (for easy birth) than is the
size of the mare. I’ve had Arabian recipient mares that carry Quarter
Horse foals very nicely. We tend to think the Arabian is too small, but if
you have one that’s adequate through her pelvis, it’s no problem,” he
“The main thing about a recipient
mare is that she be healthy and reasonable to work with. When I purchase a
recipient mare, I like to get one 4 to 8 years of age, and a good
recipient mare will stay in our herd until she’s 12 to 14, if she’s still
coming back to us at that point. The way our fee structure is, we give a
deposit back on the recipient, to try to get those mares back to us. I
probably have a few now that are 15 to 16 years-old, but they are sold if
they start to have any kind of problem.”
Freezing Embryos - Some people are
freezing embryos so they can be stored or shipped and put into a recipient
mare at a later date. “Success rate was low at first. When I was working
with this at Granada, we had some international clients interested in
buying embryos. But at that time the embryos from really good mares were
too valuable to freeze, because of the risk involved (only a 30 to 40
percent success rate). Now the success rate is more like 60 to 70
percent,” he says.
Today there’s a lot more interest in
freezing embryos, partly for international trade, or for collecting them
at different times of year and then transferring them at a more opportune
time. “For instance, we can freeze an embryo in November and then transfer
it in March. If a mare has a heavy show schedule in the spring, we can
collect it in the fall and save it for a more reasonable time.”
ET success (after the embryo is
collected and prepared) will range anywhere from 50 to 70 percent on old
mares, to more than 85 percent on young, healthy mares. “Some people will
quote figures of 90 percent. If you include all the numbers, including
embryos that are shipped out, our facility had over an 85 percent success
rate last year, and much of that comes down to good management of
recipient mares. This includes management of the recipient at the
commercial facilities that we ship embryos to. We’ve all gotten better at
managing the mares,” he says. The overall success rate for ET has improved
about 20 percent over the past 10 years.
The Process - The flushing of the
donor mare (to recover the embryo) must take place 6 to 9 days after the
mare ovulates. A catheter is placed through the mare’s cervix, to carry
the fluid. There are two passageways in the catheter. One carries the
fluid and the other puts air through, with a cuff at the end that blows up
like a tiny donut. It is inflated once you get it into the uterus, and it
acts as a plug to keep the fluid from coming out. It also keeps the
catheter from falling out while you are flushing the mare. A liter of
buffered saline flows into the uterus.
This solution is warmed to body
temperature first by putting it into a water bath for an hour. Technicians
may add calf serum or bovine serum albumin to help with viability of the
embryo. Embryos tend to be sticky, and this also coats the tubing and
glassware so the embryo won’t stick to the tube. After the liter of fluid
goes into the mare’s uterus, flowing in by gravity, it is allowed to drain
On its way out, it goes through an
embryo filter which is a little cup with a screen mesh in it. The pores in
the filter are smaller than the embryo to catch it. You may see the embryo
in that first liter of fluid you recover from the mare. If you don’t find
it in that liter, you must run in another fresh liter, or even a third or
fourth liter. Most of the time, the embryo will be in the first liter.
Flushing the mare takes about 15 minutes, then the fluid is taken into the
lab to find the embryo.
Age of the embryo and suitability
for transfer is evaluated, then it’s transferred into the recipient mare
(going through the cervix and depositing it into her uterus). Day 8 is
ideal for flushing, since this is the easiest day (embryo size), for ease
of handling and transfer. Six days post-ovulation is the earliest you can
flush a mare and recover the embryo because there’s a certain amount of
transport time. It takes about 5 days for the embryo to travel down the
fallopian tube; you can’t retrieve it until it comes down into the
When flushing the donor mare, the
process is simple. There’s actually more risk involved for the recipient
mare since she’s not in heat, and more prone to pick up infection since
the technician must open her cervix. The recipient mare must be near the
same point in her estrus cycle as the donor mare, so her uterus will be
prepared to receive and nourish the embryo. When selecting a recipient
mare for a transplant, you match the recipient with the donor mare. The
donor mare, at day 6 to 9 post-ovulation, is now out of heat, and so is
the recipient mare.
If you’re going to ship an embryo,
the procedure is similar, except that in the last step the embryo goes
into a different kind of media, and you also have to cool it. A salt
solution is always used as the flushing agent. The embryo will be fine in
this for two to three hours, but after that it needs to be in a culture
medium, that it can actually grow in. In this environment, it can be
packaged and shipped, or taken to put into a mare somewhere
With ultrasound, a person can tell
if the embryo took by the time it is 11 to 12 days old--which will be only
a few days after you’ve transferred it. You can see 90 percent of the
embryos by the time they are 11 days old, and 95 percent of them by day
12. If it’s not visible by 14 days, it probably didn’t take.
The Equine Embryo - At its earliest
stage, the embryo is very tiny but also very tough. The 8 day old embryo
is more fragile; the bigger they get, the more fragile they become. The
only ones you can safely freeze are those at day 6. Once they get to day
7, you can cool them but you can’t freeze them; there’s more fluid in the
cells by then and freezing and thawing would rupture something.
The 7 day-old embryo is about the
size of the ball on a fine-tipped ball point pen. The 8 day old embryo is
about .9 to 1.5 millimeters in size, the 9 day-old embryo is 2 to 3
millimeters, and the 10 day-old embryo is 3 to 5 millimeters in
diameter--very easy to see. The early stage embryo doubles in size from
day to day until about day 15 or 16 days, which makes it easy to see on
ultrasound any time after day 10. Mares’ embryos tend to be spherical, and
the 7 day-old embryo has the texture and appearance of a semi-transparent
golf ball, with a smooth capsule on the outer surface.
Embryo Transfer is the wave of the future
of breeding, however, the challenges presented by Mother Nature provide a
natural check to the reproduction process.
Fertility in the mare begins with ovulation. The mare naturally ovulates one ovum (egg) per 21-day cycle. In a typical breeding season, February through July, this presents six to eight opportunities for ova to be fertilized. Compared to the mare's spontaneous (unassisted) ovulation, superovulation maximizes the fertilization opportunities by inducing the development and ovulation of a greater number of follicles. This method can optimize fertility--ova mature in follicles, so a greater number of follicles means more oocytes and an increased likelihood of conceiving more foals.
With a higher probability of establishing a pregnancy, superovulation might result in the fertilization of multiple oocytes. This gives us a possible opportunity to collect more than one embryo for implanting into donor mares via embryo transfer.
Superovulation stimulates the entire follicular wave. Those follicles that might have degenerated--or not have been selected to ovulate--will go ahead and ovulate in addition to the dominant follicle.
Equine pituitary extract (EPE) has succeeded in producing multiple ovulations. This preparation consists of gonadotropins from the horse's pituitary gland. At CSU, gonadotropins are extracted and processed to yield the EPE compound. McCue defined the resulting EPE as containing "approximately 6-10% LH (luteinizing hormone) and 2-4% FSH."
He described the use of EPE to superovulate mares at CSU.
"The exact day of ovulation is determined and the mares are then short-cycled with prostaglandin (PGF2alpha) five days later and administered 30 mg. of EPE as an intramuscular injection once daily." Prostaglandin destroys the corpus luteum, and it starts the estrous cycle just prior to the beginning of the next follicular wave. EPE treatment lasts approximately six to eight days.
"When multiple follicles greater than 35 mm in diameter are detected, the mares receive 2500 IU human chorionic gonadotropin (hCG) intravenously to promote synchronous ovulations," said McCue. A mare is bred prior to ovulation and also when she ovulates, immediately after researchers detect ovulation.
Recent research has shown that EPE provides better multiple ovulation results than other hormone treatments. For example, researchers have studied the effects of gonadotropin-releasing hormone (GnRH), which helped improve ovulation rates through multiple ovulations in seasonally non-cycling mares. However, this hormone showed less-promising results on cycling mares.
At CSU, the results of superovulating 55 mares in the embryo transfer program in the 1994 and 1995 breeding seasons were an overall 2.4 ovulations per cycle, with a range from one to five. Of mares treated with EPE, 74% had multiple ovulations. Researchers elsewhere had reported as many as 10 ovulations in one mare due to EPE treatment.
Mares were bred with either shipped cooled semen or frozen-thawed semen, and pregnancies monitored with ultrasound. Results were double the number of embryos collected per donor (from the superovulated mares as compared to non-treated mares).
at CSU have investigated whether superovulating normal mares can lead to
increased pregnancy rates in mares bred to a subfertile stallion. McCue
noted that mares ovulating multiple follicles had a 67% pregnancy rate,
compared with 33% for the mares with a single follicle. This result was
for mares inseminated with a limited dose of frozen semen.
227. HORSES NOT ELIGIBLE FOR REGISTRATION (a)Horses produced by any cloning process are not eligible for registration. Cloning is defined as any method by which the genetic material of an unfertilized egg or an embryo is removed, replaced by genetic material taken from another organism, added to with genetic material from another organism, or otherwise modified by any means in order to produce a live foal.
The only trouble with this is that any offspring of
a clone produced by normal breeding methods is not going to be eligible
for registration, as a result of the sire or dam having been ineligible -
even though clones are just "twins separated in time". It's going to be
Another Gelding to Breed!