{"id":35689,"date":"2016-04-01T00:32:28","date_gmt":"2016-03-31T21:32:28","guid":{"rendered":"http:\/\/www.alassalah.com\/en\/?p=35689"},"modified":"2016-04-02T00:40:22","modified_gmt":"2016-04-01T21:40:22","slug":"twins-in-horses","status":"publish","type":"post","link":"https:\/\/www.alassalah.com\/en\/2016\/04\/01\/twins-in-horses\/","title":{"rendered":"Twins in Horses !"},"content":{"rendered":"
By Heather Smith Thomas<\/span><\/span><\/h5>\n

Although it is possible for a mare to deliver the occasional set of healthy twin foals, her uterus is not designed to support two pregnancies simultaneously. <\/span><\/p>\n

Veterinarians discuss methods for detecting and reducing twins<\/span><\/h4>\n

Twins are a novelty, especially the equine variety, and while we\u2019ve all heard heartwarming stories about special cases in which both foals survived, the truth is less than one in 100 twin pregnancies results in such a fortunate outcome. Why the miserable odds? Simply, the mare\u2019s uterus is not designed to support two pregnancies simultaneously, says Juan Samper, DVM, PhD, an equine reproduction specialist located in Langley, British Columbia.\u00a0<\/span><\/p>\n

This is why conscientious horse breeders try to avoid this situation altogether, and it is also one of several reasons why veterinarians should examine mares 14 days after breeding, says Ahmed Tibary, DVM, PhD, Dipl. ACT, professor of theriogenology in Washington State University\u2019s Department of Veterinary Clinical Sciences.\u00a0<\/span><\/p>\n

We visited with Samper and Tibary to understand why twin pregnancies occur, why they\u2019re dangerous, and how early detection and intervention can help you avoid a two-for-one which could prove dangerous or even deadly. \u00a0<\/span><\/p>\n

Reasons for Twins<\/span><\/h4>\n

In a normal conception, a follicle from the mare\u2019s ovaries matures into an ovum that is then fertilized by the stallion\u2019s sperm. Most twin pregnancies occur when sperm fertilize two eggs released from two different follicles as a mare double-ovulates.\u00a0<\/span><\/p>\n

Thoroughbreds and Warmbloods are notorious multiple ovulators and, thus, tend to conceive twins more frequently than other breeds. The percentage of twin pregnancies among Thoroughbreds is about 30%, depending on the mare\u2019s history and age, while in Quarter Horses, for example, it\u2019s only about 5%, says Tibary.\u00a0<\/span><\/p>\n

No matter the breed, double ovulations are more likely to occur in nonlactating mares (i.e., they don\u2019t have foals at their sides) at the peak of breeding season. \u201cA mare that has double-ovulated in one cycle has a 38% chance of double ovulation on the next cycle,\u201d Tibary says. \u201cI recall working with three mares (two Thoroughbreds and a Warmblood) that double-ovulated on more than 80% of their cycles.\u201d He adds that the chances for double ovulation to result in twin pregnancies are highest in young mares when they are most fertile, which is from about age 6 to 8.<\/span><\/p>\n

\u201cRecent studies with Thoroughbreds in Newmarket and Kentucky show that older barren (nonpregnant) mares are more likely to double-ovulate than young lactating mares,\u201d Tibary says. \u201cGenetics and nutrition play important roles in whether a mare will double ovulate.\u201d<\/span><\/p>\n

If your mare does ovulate more than one follicle on a cycle that you hope to breed her, it\u2019s important to monitor her closely. \u201cIt\u2019s also crucial to know whether she ovulates them at the same time or a few days apart,\u201d Samper says. \u201cYou have to decide when you will do the initial pregnancy exam on that mare. When two ovulations occur within the same day (and you breed the mare), it\u2019s best to check the mare at 14 or 15 days after the ovulations were detected. At that time it is a very simple procedure to manually reduce the twin pregnancy to a single embryo.\u201d<\/span><\/p>\n

\u201cIf twins are caught before 16 days, the common technique is to manually reduce them by squeezing one of the embryonic vesicles.\u201d<\/span><\/p>\n

Twin Position\u00a0<\/span><\/h4>\n

About six days after conception the relatively motionless embryo descends into the uterus. It becomes more active about Day 9 and moves around the uterus from the tip of one horn to the tip of the other several times during the next few days. This transuterine migration is a signal to the mare to recognize that she is pregnant, triggering processes that will help her maintain the pregnancy and prevent her from coming into heat again. On about Day 16 or 17 the embryo stops moving around and \u201cfixes\u201d at the base of one of the uterine horns. When there are two embryos, most of them fix in the same horn; only about 30% end up in different horns, Tibary says.<\/span><\/p>\n

What dictates this grouping or separation is embryo size: Different-sized embryos tend to fix in the same horn, while those of similar size tend to fix in the opposite horns. \u201cThis is due to the fact that fixation of one (usually the older, larger one) impairs the mobility of the other and tends to force it to fix on the same horn,\u201d explains Tibary.<\/span><\/p>\n

When twins fix in the same horn, more than 80% of those pregnancies are either lost or they resolve naturally, the latter meaning that \u201cthe larger one will grow and undermine the other one, and the smaller, weaker one will die,\u201d says Samper. By Day 30 to 35 this process will have finished.<\/span><\/p>\n

When twins fix in opposite horns, the embryos often survive beyond Day 40 and are aborted between five and nine months\u2019 gestation or, in rare instances, are carried long enough to be born alive.\u00a0<\/span><\/p>\n

Dealing with Twins\u00a0<\/span><\/h4>\n

It\u2019s not the end of the world if your veterinarian detects twins early, but such cases do become more complicated the longer you wait. \u201cWe know that the most dangerous twins (for the mare) are those that fix in different horns,\u201d Tibary says. Besides the longer survival, generally resulting in late-term abortion, they can also be born prematurely with complications at birth.<\/span><\/p>\n

Checking mares for pregnancy and twinning at 14 days post-ovulation becomes especially critical if you already know the mare tends to double ovulate, says Tibary. If you don\u2019t know the mare\u2019s exact ovulation date, have your veterinarian examine her 16 days after the last stallion cover.<\/span><\/p>\n

\u201cIf twins are caught before 16 days, the common technique is to manually reduce them by squeezing one of the (embryonic) vesicles,\u201d Tibary says. In the hands of an experienced equine theriogenologist, this method yields a success rate of almost 100%\u2014safely maintaining one live fetus, especially in mares younger than 15 years.\u00a0<\/span><\/p>\n

In a recent Kentucky study in which practitioners assessed all the twins Rood & Riddle Equine Hospital had reduced, manual twin reduction had no negative effect on the pregnancy, if done correctly. \u201cWith ultrasound we can monitor the uterus as we are doing this and know for sure that we have removed one of the embryos,\u201d Tibary says.\u00a0<\/span><\/p>\n

After 25 days, he explains, veterinarians generally don\u2019t try to squeeze or rupture one of the vesicles and, instead, try to disturb and dislodge it (in which case it will die). \u201cThe problem at that stage of pregnancy is that the vesicle is larger, with more fluid,\u201d he explains. The release of this fluid into the uterus can affect the remaining embryo\u2019s development.<\/span><\/p>\n

For that reason, it\u2019s good that the vesicle at this stage is also tougher and more resistant; however, this means the practitioner must apply more pressure and manipulation to disrupt it so it will not be viable. \u201cThis (manipulation) creates more inflammation and may have an adverse effect on the other conceptus,\u201d Tibary says. \u201cAt that point, additional treatments will be required to reduce inflammation and try to maintain progesterone levels so the pregnancy won\u2019t be lost. The cost of maintaining the pregnancy is greater.\u201d<\/span><\/p>\n

Another technique veterinarians can use if the pregnancy is 25 to about 50 to 60 days is transvaginal ultrasound-guided aspiration (TUGA). \u201cThe practitioner places a special ultrasound probe into the mare\u2019s vagina, and with one hand in the rectum the probe is directed to one of the vesicles,\u201d Tibary says. \u201cThe rigid handle of the ultrasound probe has a channel for a very long needle. We can pop it through the vaginal wall and into the uterine cavity\u2014into the embryonic vesicle\u2014to aspirate it,\u201d or draw it out. This process\u2019 success rate ranges from about 40 to 70%, he adds, depending on when you do it and the location of the embryo (same horn or opposite horn from the other embryo).<\/span><\/p>\n

\u201cSuccess is mare-dependent,\u201d he adds. \u201cSome mares are more difficult because their uterus is larger and it\u2019s hard to stabilize the needle. This procedure requires sedation and, sometimes, drugs to relax the rectum so manipulation can be accomplished without injuring the mare.\u201d<\/span><\/p>\n

Another technique, applied when the mare is 110 to 150 days pregnant, terminates the fetus using ultrasound guidance with the needle inserted through the abdomen rather than through the vagina\u2014a more dangerous process for the mare.\u00a0<\/span><\/p>\n

\u201cThere is always risk to the other fetus; the success rate with this technique at this stage of pregnancy is 40 to 50%,\u201d Tibary says. \u201cThere is risk that both (twins) will die, or that the stab is not correctly done and the fetus survives longer. At this advanced stage, the dead fetus will become a mummy. We end up with a fetus that\u2019s normal and one that\u2019s mummified and remains small,\u201d delivered in a small sac separate from the live foal.<\/span><\/p>\n

There is another method veterinarians use when it\u2019s too late for traditional techniques: \u201cThis method is surgical, using a flank incision,\u201d says Tibary. \u201cThe surgeon reaches inside the abdomen, finds the fetus (feeling through the uterine wall) and grasps the head between the thumb and index finger. With a rocking motion, the neck is snapped. The fetus will die a few days later. This can be done at some point between 60 to 150 days of pregnancy with 50 to 60% success rate.\u201d<\/span><\/p>\n

Importance of a Pregnancy Exam<\/span><\/h4>\n

There is always a chance that a veterinarian might miss detecting the younger, smaller second embryo upon examining the mare at 14 days. \u201cThere are synchronous (occurring less than 24 hours apart) and asynchronous (occurring more than 24 hours apart) double ovulations,\u201d Tibary says. \u201cIf they occur within 24 hours of each other there\u2019s a good chance we\u2019ll see both embryos at 14 days. But if the second ovulation occurs three to four days later, the second egg can still be fertilized, especially if you are using a very fertile stallion.\u201d<\/span><\/p>\n

Therefore, a veterinarian should perform a more thorough examination than just determining whether the mare is pregnant. \u201cEvery millimeter of the uterus should be examined,\u201d Tibary says. \u201cThe second embryo may be hidden, or a different size, or in the other horn. If we find only one, we shouldn\u2019t end the exam; we need to check the ovaries and make sure the mare did not have two ovulations.\u201d\u00a0<\/span><\/p>\n

Another reason veterinarians have historically missed picking up on twins is that it\u2019s difficult to see two fetuses when they are so close together. \u201cNow with Doppler ultrasound (which shows blood flow) we can pinpoint where the heart is,\u201d Tibary says. \u201cIf we see two heartbeats we know there are twins.\u201d<\/span><\/p>\n

Risks to the Mare\u00a0<\/span><\/h4>\n

While we\u2019ve focused mainly on saving one foal of a twin pregnancy, remember that your mare\u2019s life also is at stake: If she retains both fetuses and is set to deliver two foals, you risk losing all three horses. \u201cIf you\u2019re lucky, the mare will deliver the two foals with no problem, one after the other,\u201d says Samper. \u201cBut there\u2019s the chance that both foals are tying to come through the birth canal at the same time, and this creates a terrible dystocia,\u201d or difficult birth.\u00a0<\/span><\/p>\n

\u201cThe mare that foals twins will often retain the placenta(s),\u201d says Samper, setting off a potentially deadly metabolic cascade of events. \u201cThese mares may end up with laminitis if you\u2019re not careful.\u201d Even though some twins survive and do well, they are the exception. Most breeders don\u2019t want to risk the mare\u2019s well-being to find out if they\u2019re one of select few.<\/span><\/p>\n

Take-Home Message\u00a0<\/span><\/h4>\n

Early pregnancy diagnosis 13 to 15 days after ovulation is important, along with ovary evaluation, to determine whether a mare ovulated twice and could be harboring twins. If your veterinarian detects twin embryos, discuss with him or her the various appropriate management options, for the stage at which they are discovered.<\/span><\/p>\n

Src:\u00a0thehorse.com<\/h5>\n","protected":false},"excerpt":{"rendered":"

By Heather Smith Thomas Although it is possible for a mare to deliver the occasional set of healthy twin foals, her uterus is not designed to support two pregnancies simultaneously. Veterinarians discuss methods for detecting and reducing twins Twins are a novelty, especially the equine variety, and while we\u2019ve all heard heartwarming stories about special …<\/p>\n","protected":false},"author":139,"featured_media":35691,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[381,374],"tags":[],"_links":{"self":[{"href":"https:\/\/www.alassalah.com\/en\/wp-json\/wp\/v2\/posts\/35689"}],"collection":[{"href":"https:\/\/www.alassalah.com\/en\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.alassalah.com\/en\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.alassalah.com\/en\/wp-json\/wp\/v2\/users\/139"}],"replies":[{"embeddable":true,"href":"https:\/\/www.alassalah.com\/en\/wp-json\/wp\/v2\/comments?post=35689"}],"version-history":[{"count":0,"href":"https:\/\/www.alassalah.com\/en\/wp-json\/wp\/v2\/posts\/35689\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.alassalah.com\/en\/wp-json\/wp\/v2\/media\/35691"}],"wp:attachment":[{"href":"https:\/\/www.alassalah.com\/en\/wp-json\/wp\/v2\/media?parent=35689"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.alassalah.com\/en\/wp-json\/wp\/v2\/categories?post=35689"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.alassalah.com\/en\/wp-json\/wp\/v2\/tags?post=35689"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}