Embryo Tranfer, Again...

Recently, the topic of allowing multiple foals from mares came up on Haynet, the on-line forum for discussing model horses. A newcomer to PA made the statement that she allowed unlimited numbers of foals from mares because "ET technology made it possible". A lively discussion followed about the realism of unlimited foals. The following is an excerpt from a post written by hobbyist Jackie Arns. For those that do not know Jackie, she is a fourth-year veterinary student at Cornell specializing in equine reproduction. She has worked in Cornell's Theriogenology (reproduction) department, and has been involved with embryo transfer. She offered the following information for those doing pedigree assignment:

"What I've read today from everyone who's been replying has been a combination of truth, wishful thinking, and misunderstandings. So.... here we go....equine theriogenology in a nutshell!

EMBRYO TRANSFER (ET) -- This is the technique you use when you feel you have a genetically superior female, or your chosen female cannot carry a pregnancy for some reason.

  1. Again, cattle folks are way way ahead of horse breeds! But some of the reasons are ones of biology. In theory, when using ET, you superovulate your female, breed her, flush out her embryos after a few days and implant the embryos into other females. This is much harder than it sounds.
  2. 'Superovulation' in mares doesn't really happen. When you superovulate a cow, you can get 6-8 follicles to ovulate at the same time and theoretically, 6-8 embryos on that flush. With mares, if you get one follicle to ovulate, you take it. If you get two, you celebrate your amazing fortune. Yes, some mares will occasionally have multiple ovulations normally. But these do not happen as predictably as they do with cattle.
  3. You must have several 'recipient' mares (those who are going to get the embryos) who are at the same stage of estrus as your 'donor mare'(the one whom the embryo is coming from). You can't implant an embryo into any old mare. She's got to be at the same place in her cycle or you're wasting your money. At Cornell, we achieve synchronicity between our recipients and donors mainly by trying to manipulate their hormones....we use a lot of LH and prostaglandin 'short cycling' mares.
  4. Your potential offspring had better be worth a lot to you because you're going to be spending a lot of time and money producing horses this way."

Give this information, it is obvious that many have misconceptions of just what is involved in Embryo Transfer. It is not enough to be able to 'transfer' the embryos to donor mares. The mares must also be made to superovulate -- something that, as Jackie pointed out, is not currently possible. The idea that females have infinite ovum that can be harvested and implanted into donors is unrealistic; the ovum still must be fertilized in the original mare's follicle and then flushed for implantation, and that limits the number of possible embryos to two. Statistical probability makes even that number less likely.

IPABRA does not ban the practice of multiple foals from mares. That is still the choice of each individual. However, those interested in strict standards of realism should be aware that unlimited foals from mares cannot currently by justified by "advances in technology".

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