From: Barb
Jessica;
From a post you responded to on E-L: you mentioned that a mare that has twins generally will twin in the future and that there is little that can be done to prevent twinning. I seem to recall my vet telling me that if he finds out about the twins earlier enough in the pregnancy he will abort one of the twins leaving the other to develop to full term. Did I misunderstand him or is he doing something fairly new? Or perhaps, this procedure is risky? Your comments/thoughts would be appreciated.
Barb
It's very common for vets to "pinch" one embryo so as to end a double pregnancy and allow one foal to develop to full term. New technologies have made it much easier to detect the presence of twins at an early date -- sometimes as early as ten days after conception! More and more veterinarians are travelling around with portable ultrasound machines, which -- at least for the first 60 days -- make it very easy to detect twins, so in theory it should be a simple matter to eliminate twinning.
There are a few problems, though -- for one, the window of opportunity is not enormous. If you want to get rid of ONE of two conceptions while maintaining the second one, you must act before the 17th day after conception. After that, you can still get rid of one, but you are likely to have a strong effect on the uterine environment, and lose BOTH.
Still, that's preferable to the alternative -- if you abort the mare, which you can do in the first forty days, you can begin again. Your mare will probably be able to conceive again during that breeding season -- if you wait until later to abort the mare, or wait until she aborts the foals herself, which can be at ANY time up until a normal delivery SHOULD take place, you put a lot of stress on her uterus and you eliminate the chance of breeding her that year and possibly the next year as well.
Even after a few months, if the mare is aborted and her uterus flushed with saline and antibiotics to help clean out any infection, it takes several more months -- sometimes the entire breeding season -- for the mare's uterus to recover. And if there is no intervention at all, whether the twins abort around day 200 as they often do, or whether the mare continues to carry them, it takes a LONG time for a mare to recover from carrying twins, whether they abort, are born dead, or are born alive. And even if they are both born alive, which is unusual, you aren't likely to keep them alive -- and even if you do, they will grow into undersized, not-very-useful horses, and you will STILL have stressed your mare unnecessarily, impairing her fertility in the short term and possibly also in the long term.
Some mares tend to double-ovulate every time, and these are at particular risk for twinning. It's always best to check, double-check, and triple-check an in-foal mare, and do it early enough so that if she is twinning, you can do something about it while there is still time. In nature, twinning mares would almost certainly be barren mares; we can interfere with the process and get offspring from such mares, but we can't keep those offspring from inheriting the tendency to have double ovulations. So you could say that this is a problem that our new abilities and technologies are making worse. If you are breeding ONE foal for your own use, this may not matter, but if you are creating future breeding stock... it's something to think about.
In the instance mentioned on E-L, it wasn't clear why the vet had failed to notice the twins -- but if he wasn't called in to check the mare until she was, say, two months along, it could have been almost impossible to detect the double pregnancy using ultrasound (the position of the foals at this time makes visualization very difficult).
So in answer to your original question (aren't you sorry you asked!), no, the "pinching" of the second embryo is a well-known, commonly accepted practice, and your guess is as good as mine as to why it wasn't done in this particular case.
- Jessica
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