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By Jos Mottershead and Kathy St. MartinYou've read all the articles at Equine-Reproduction.com, your mare was in heat, you jumped through all the various hoops you needed to in order to get your mare bred, and now you're excitedly awaiting your veterinarian's verdict as to whether or not she is pregnant. The ultrasound screen shows a strange selection of white, grey and black blobs, and you anxiously await the veterinarian's explanation of what you are looking at... But when the word comes, it's not what you wanted to hear... TWINS!!! Oh no! Now what?
If it is determined that what is present is truly twins, the next step will depend greatly upon what pregnancy stage the mare was at when this ultrasound was performed. Ideally, the mare is being checked prior to the stage at which the conceptus becomes "fixed" within the uterus. In most full-size horse-breed mares, this occurs 16 days post-ovulation, and in most pony mares 15 days post-ovulation ("fixation" generally occurs a day earlier in ponies than in horses). Checking prior to the fixation of the conceptus allows for easier manipulation of one (or both) of the twins in order to enable a manual reduction to a singleton pregnancy. In some circumstances, once fixation has occurred, such a reduction is made more difficult, and the success rate of maintaining even a single pregnancy is reduced. Twins detected prior to conceptus fixation Twins detected prior to conceptus fixation can usually be successfully reduced to a singleton pregnancy with reasonable ease. In the event they are situated immediately adjacent to each other, one can attempt to manipulate one, or return to the same mare about 15 minutes later, and often the conceptuses will have separated of their own accord. One of the twins can then be maneuvered towards the distal (tip) end of the uterine horn, and reduced by exerting pressure using either the thumb and forefinger, or more usually the ultrasound transducer against the pelvis. One question that may arise is "which conceptus should be 'pinched', the larger or the smaller?" if there is a size difference. There are different schools of thought on this subject, with one suggesting that the larger conceptus will reduce more easily, thereby causing less irritation to the uterus. With less irritation, a higher pregnancy maintenance level may be result. The opposing school suggests that the smaller conceptus may already be in the process of reducing naturally, so reduction of the larger one may result in loss of both pregnancies. Other factors that require consideration include position of the conceptus' and the ease with which they can be reached by the manipulator. Irritation of the uterine lining results in the release of a hormone called prostaglandin. This hormone is responsible for the destruction of the Corpus Luteum ("CL"), which is in turn responsible for the secretion of the essential pregnancy-supporting hormone, progesterone. Without progesterone, the pregnancy - twin or otherwise - is doomed. The use about 30-60 minutes prior to attempting twin pregnancy reduction of drugs such as flunixin meglumine ("Banamine") that inhibit the release of prostaglandin, may also be valuable in supporting pregnancy maintenance. Twins detected after conceptus fixation Twins detected after conceptus fixation must be treated differently from those identified prior to fixation. The position of the twins can have a significant impact on the likely outcome. If the twins are the same size, and located in a non-adjacent position (e.g. opposite horns of the uterus), then the most convenient should be selected for reduction. If the twins are of a different size, and located in a non-adjacent position, then as with same size conceptus, the most convenient and non-viable appearing conceptus should be selected for reduction. If the twins are touching, it become a little more complicated... If they are of the same size, one may elect to use a luteolytic dose of prostaglandin to reduce both twins, and rebreed the mare (i.e. start all over again). There is a significantly lower success rate in reduction to a singleton pregnancy in this situation. There is also a demonstrated maintenance of both pregnancies of up to 27%1, which is considered too high a risk to contemplate attempting to preserve either pregnancy. Of course one may attempt a single reduction by pinching off one pregnancy. This however, can be difficult to achieve without damage to the second pregnancy resulting in loss of that conceptus also. If this latter rout is followed, it is essential that follow-up evaluations be performed no later than day 28 post-ovulation. If at that time, there are still 2 pregnancies remaining, it is advisable that prostaglandin be used immediately to terminate both pregnancies and cause the mare to return to estrus. A pregnancy that is continued beyond about day 30 and subsequently lost (prior to about day 120), may result in the mare not returning to estrus until 120-150 days after the ovulation that resulted in the pregnancy(ies) - a significant problem if you want to rebreed her the same season!
It is worth noting that there is a higher incidence of twinning in older barren mares. Nature is attempting to promote the establishment of a pregnancy in these mares, who may - as a result of age-related changes - be sub-fertile. It is therefore very important to do a thorough check for twin pregnancies in such mares. It is equally noteworthy that mares that have once had a double ovulation (or twinned) are more likely to repeat this, and therefore also warrant a careful pregnancy examination. Post-foaling mares up to about 80 days after foaling are the least likely group to produce double ovulations, while maiden mares fall into the middle range. Ponies are less likely to produce multiple ovulations, while Thoroughbreds and Draught breeds are more likely to produce them.
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This article was produced by Jos Mottershead & and Kathy St.Martin of Equine-Reproduction.com Imitated by some - duplicated by none!
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