Double Trouble: Twin Pregnancies
Twins may seem like double the fun, but in reality a twin pregnancy can result in the death of both foals and the mare.
Twin pregnancies can occur if there are multiple ovulations around the time of insemination or mating. The frequency of twin conceptions varies between breeds and individual mares, with mares that have previously conceived twins at a higher risk of future twin pregnancies.
Why Twins are a Problem
The mare’s uterus is designed to provide enough nutrients to support one foal. With twins inadequate nutrients would be supplied to each foal with several possible outcomes. In some cases one or both of the embryos may be resorbed within the uterus early in the pregnancy. If resorption does not occur, late term abortions typically result. If the twins do survive to full term pregnancy the most common outcome is the birth of two developmentally stunted foals that adapt poorly to life outside of the uterus and subsequently die. In atypical cases, one foal may be born normal while the other foal dies. It is extremely rare for both twins to live and develop into adults.
The health of the mare can be seriously compromised when twins are carried into late term pregnancy. The mare’s uterus is capable of extremely strong contractions and in trying to give birth to two foals the reproductive tract can easily be damaged. This can result in such complications as a ruptured uterus, ruptured uterine arteries, and recto-vaginal tears. Furthermore, mare’s that carry twins are at a higher risk of developing conditions such as metritis and retained foetal membranes. These conditions can not only lead to future breeding difficulties but in many cases the death of the mare.
A final consideration is the financial costs that may be incurred in treating twin foals that are born alive, treating any complications in the mare, as well as the cost of getting the mare pregnant in the future if there is damage to the reproductive tract.
Detection and Treatment of Twins
Before breeding your mare it is important to perform a pre-breeding examination of the reproductive tract. This will not only identify any potential problems with conception but will also allow identification of cysts within the wall of the uterus which have the potential to be confused for a second embryo.
The identified risks of twin pregnancies highlight the importance of early pregnancy ultrasounds. An ultrasound exam is recommended at day 15 of the pregnancy. At this age embryos are able to be identified via rectal ultrasound and are still mobile within the uterus. If twins are detected this mobility allows the veterinarian to separate the embryos so that one embryo can be ablated, hopefully, without harm to the other. If both embryos are lost the mare will potentially return to oestrus within 10 days.
It is important that another ultrasound exam is performed at day 28 and before day 35. This allows for the identification of any twin pregnancies that may have been missed at the initial scan. This can occasionally occur as the mare has the ability to ovulate up to 5 days apart and conceive more than once. Embryos can just begin to be seen via ultrasound at day 10, meaning that a day 15 scan may identify one 15 day old embryo while another 10 day old embryo could easily be missed.
It is at day 35 that the pregnant mares uterus begins to produce pregnancy hormones. Loss of both embryos after this point by physical ablation or by medical abortion can result in the persistence of pregnancy hormones for an extended period of time, preventing normal oestrus cycles for months. This can result in a whole breeding season being lost.
If twins are detected later in the pregnancy it is often necessary, and unavoidable, to terminate both pregnancies to give your mare the best chance of becoming pregnant again. Your veterinarian can employ a range of techniques to achieve this outcome.
Prevention of Twins
Unfortunately, the number of ovulations a mare will have cannot reliably be controlled, however, by having pre-insemination scans up to the day of ovulation your veterinarian will be able to predict the number of potential oocytes that have been ovulated and therefore the potential risk of twins. Still, it is always necessary to have an ultrasound exam at day 15, at which time the presence of twins can be dealt with most effectively. It is also recommended to have a minimum of one further scan prior to day 35.
Allowing your mare to carry twins comes with unacceptable and unnecessary risks. Having the minimum number of ultrasound examinations at day 15 and day 28 of pregnancy should be a part of every mare’s pregnancy. By following the above recommendations you will not only help prevent the serious complications associated with twin pregnancies but facilitate a successful breeding season.