Can A Mare Abort One Twin?

Last Updated on May 26, 2022

Twins are very rare in horses and it’s not uncommon for one or both foals to die during birth. So, you may wonder, can a mare abort one twin? Though twin foals are adorable, they are undesirable due to the low survival rate.

Only a handful of mares will successfully birth both foals, with both of them surviving. Twins in horses are dangerous, as there are many things that can go wrong for the mare and foals. In cases, where both foals survive, they normally have numerous health problems.

Twin Foals In Horses – Can A Mare Abort One Twin?

Twin foals are very rare, as most mares will only give birth to one foal at a time.  In equine twin pregnancies, 60% will give birth to a live single foal, 31% will abort both foals and just 9% will carry both twins to term. Of the 9% that carry both to term, 64.5% will give birth to two stillborn foals, 21% will birth one live foal and one stillborn foal and just 14.5% will birth two live foals.

Twin births only make up 1-2% of all equine births. Due to how large foals are at birth, it is very difficult for a mare to safely carry both foals to term.

Not only is it dangerous for the foals, as it is rare for both foals to survive, but it is also dangerous for the mare as well. In some cases, the mare will die while trying to give birth to twins, often resulting in the death of the foals as well. In most cases, veterinarian intervention will happen if a mare is pregnant with twins. It is generally too risky to have a horse carry twins to term.

Twin Foals In Horses

What To Do If Your Mare Is Pregnant With Twins?

If your mare becomes pregnant with twins, you will need to talk to your veterinarian to find out what the best option is for your mare. Though it is not the desirable choice, it is often the safest choice to abort one or both foals. It is just oftentimes too dangerous for a horse to have twins.

If twins are detected by ultrasonography per rectum at less than 30 days, action is generally taken by the veterinarian. In some cases, if twins are discovered early enough in the pregnancy, one embryo can manually be removed. If both embryos end up destroyed, a mare can be re-breed if the embryos are destroyed prior to the 30th day of pregnancy.

In some cases, the second foal may not be detected until later in the pregnancy. In these cases, manual reduction may be used depending on the circumstances or a horse may carry her twins to term without intervention. Sometimes, owners will choose for their mare to carry both twins to term if the mare and pregnancy are both deemed healthy, however, this is still risky.

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Can A Mare Abort One Twin?

A mare is capable of aborting one twin in order for the other embryo to survive. A mare can abort one twin to a viable singleton in the first 60 days of gestation, which can result in the birth of one healthy foal. Visible abortions tend to occur within seven to nine months of pregnancy.

A mare may display signs of an impending abortion by premature mammary gland development. In some cases, a mare’s body may naturally abort both embryos. In some cases, manual reduction may be performed for the mare’s sake.

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Manual Reduction – Can A Mare Abort One Twin?

Due to the risk of abortion and dystocia in a mare pregnant with twins,  reduction to one embryo by manual crushing via rectum is recommended. This procedure will happen within 30 days of ovulation. This is done for the safety of the mare, as the chances of both foals and mare being healthy at birth are low.

If twins are detected between 30–60 days of gestation, transvaginal aspiration of one embryo may result in a viable birth of one foal. Cervical dislocation of one fetus may be performed around approximately 60 days of gestation.

Intracardiac injection of potassium chloride or procaine penicillin, by the use of transabdominal ultrasonography, may be used at 110 days of gestation on one twin.

The success rates of manual reduction vary depending on which procedure is performed, the veterinarian’s experience, and the individual pregnancy. After performing twin reduction, the pregnancy should be sonographically monitored on a regular basis.

Natural Reduction

Natural or biological reduction occurs when a mare naturally eliminates one or both of the embryos for a better chance of survival. The natural reduction generally doesn’t occur until after day 11 of gestation. The actual process of the natural reduction in horses is not known.

If natural reduction occurs, excess embryos are eliminated and one viable embryo will continue to develop. The one surviving embryonic vesicle continues to grow and develop normally in appearance. The only potential difference between a singleton pregnancy and a natural reduction is vesicle orientation.

Twins Surviving Birth – Can A Mare Abort One Twin?

In very rare cases, a mare may carry both horses to full term and safely deliver both foals. Even if the mare and twins survive, complications are still likely to occur.

Twin foals are generally smaller at birth and often exhibit health problems. They generally will need additional veterinarian care and will often have to be monitored around the clock for the first few weeks. If twins are able to survive the first few weeks, they generally have a much higher chance to make it into adulthood.

Twins In Horses

Twins in horses are very rare and sadly, most of the time both foals will not survive. It is not uncommon for a mare to abort one or both foals for a better survival chance.

Do you have any questions regarding can a mare abort one twin? If so, please ask any questions regarding twin pregnancy in horses in the comments.


What is the Most Common Non-Infectious Cause of Abortion in a Mare?

The most common result of a non-infectious abortion in horses is twins. A twin pregnancy is very dangerous for the mare and foals, as many complications and death can occur.

How Do I Know if My Mare is Aborted?

If your mare has aborted a foal, you may notice signs such as premature mammary gland development, fever, colic, purulent vulvar discharge, swelling of limbs, depression and prolonged pregnancy. In some cases, you may see the aborted fetus or you may find the dead fetus in utero via ultrasound.

What Can Cause a Mare to Abort?

A mare may abort if she is experiencing an infectious pregnancy or she is carrying twins. In addition, gene mutations, stress, Mare Reproductive Loss Syndrome, lack of proper nutrients and umbilical cord abnormalities may lead to abortion.

What Causes Placentitis in Mares?

Placentitis happens from a bacterial or fungal infection that enters the mare via the vagina and breaches the cervical barrier. Aspiration of air and feces into the vagina can happen in mares that have poor conformation or an injury to the cervix or her vulvar opening.