COW: Too Pregnant

Breeding season is now well upon us. Here is an interesting ultrasound of a mare with 14 day twin pregnancies. Being the parent of twin boys, I have often heard the expression, ‘Congratulations, two for the price of one.’ While that is a false statement in people, it is exponentially more false in horses. The unfortunate reality is that horses do not do well with twin pregnancies. Often, both pregnancies are lost somewhere along the way so that neither one survives. Of those that survive to term, the foals are often either born pre-mature and/or extremely weak. Typically, of those that survive to term, one of the foals is either born dead or dies shortly after birth. Often the mare experiences complication with foaling as well. It is quite rare to have twin foals survive to weaning.

All that to say that twin pregnancies in horses are not good. As a result, when we encounter twin pregnancies early on, we attempt to reduce them to a single pregnancy. Early pregnancy diagnosis with ultrasound is key to successfully managing twin pregnancies. This is one of the primary reasons to pregnancy check mares 14 days after ovulation. When the vesicles are small (less than 1.5 cm), like they are in this image, one of the pregnancies can be ‘pinched’ off with pretty good success. With one of the vesicles pinched off, the other one can go on and develop into a normal healthy foal, just as if it had started as a single pregnancy.

One of the questions we are often faced with when pinching twins is, which one do you pinch? The rule of thumb is to pinch the smaller one. Inevitably, halter horse people want the one that is a colt pinched, performance horse people want the filly pinched and paint horse people want the one without color pinched. Unfortunately, we don’t yet have the technology to easily distinguish those factors so we usually just try to do the smaller one.

Early diagnosis of twin pregnancies is key to success. If not identified and pinched early, there are other options for reducing them to a single pregnancy, but those options are much more complicated with much lower success rates.