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Embryo Transfer

A recipe to take a two-week old embryo and place it inside another uterus.

A high tech way to have a valuable mare produce more than one foal each season. Embryo transfer is a tedious and exacting method starting with breeding the prize mare and stallion. After an egg matures the ovarian follicle ruptures, allowing the egg to be swept up into the Fallopian tube where fertilization will occur if spermatozoa are present. As the newly formed embryo continues to travel it enters the uterus, floating freely in the uterine horn until sixteen days after ovulation at which time it finds a place in the uterus to attach itself.

Before sixteen days the free-floating embryo can be harvested by flushing the mare’s uterus with a special nutrient solution, best done around eight days post ovulation when the embryo is so tiny a particular dissection microscope is needed to recognize the thing. The mare is flushed three times to dispel the floating unplanted embryo, and every aliquot of the solution must be examined under the microscope to see where it is. After being sucked into a glass pipette, and placed in a container of warm solution for temporary safekeeping, the embryo is ready to be put into the recipient mare's uterus.

The recipient mare must be prepared for surgery to receive the found embryo, this gal's hormonally manipulated to be in sequence with mama horse. I need to put this baby inside the recipient's uterus, in this case, her right horn, using the right flank approach.

An incision on the horse’s side in front of her pelvic bone is a good place to go in to grab the uterine horn. Pushing my gloved hand through the incision, I dropped my hand and wrist inside the mare's abdomen, swishing my hand back and forth feeling for a kielbasa sausage. Finding the thing, I exteriorized it, pulling some of it out into the light so I could make a hole for the baby. I needed to insert the found embryo inside this mare’s uterus.

Leaving my left hand around the horn to keep it from slipping back inside I grabbed my scalpel blade and punched a small hole into the uterus. Using mosquito hemostats, I pushed through my cut to make sure I was fully inside the uterus itself. Satisfied, I set the hemostats down, picked up the embryo still inside the pipette, pushed the glass tube through my uterine incision, very gently injecting the baby into a new uterine environment. But this was not the uterus it was fertilized in; this was its new home. The uterine horn is dropped back into the abdomen, and the large incision on her side sutured.

If all is in place, the transplanted embryo will attach to the new uterus in the next week or so, the pregnancy will maintain itself, and the prize mare's next egg can be fertilized and harvested too.

This is a blastocyst, a growing fertilized baby foal eight days after conception. Being fertilized just over a week ago, this fellow is floating up and down the uterus, looking for a place to settle and grow, ready to be born in eleven more months. But I can bring him out right now by flooding the uterus and examining every aliquot of recovered fluid until I see this little goober in my microscope. That's the hardest part of embryo transfer, going through a couple liters of liquid a little at a time until I find the prize.


This fellow shows mechanical damage, someone was too rough on this blastocyst trying to suck him up through the pipette. The damage is minimal though, and a healthy baby should come about in eleven months.

Look how easy it is to damage a blastocyst when sucking it up with the pipette.

This is a genetically defective embryo, cells are swollen and there are several areas void of cells. These usually do not provide a viable pregnancy. If implanted this one won't make it to the first month.

I just dropped the recipient's uterine horn back inside. Now it's time to do a two-layer closure on this girl's flank.






Audiobook coming soon



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