When a Mare Has Twins - Is It a Miracle or Double Trouble

From the January 2014 issue of The Stable Magazine – www.thestablemagazine.com/january 2014

The general consensus of twinning in mares is that twins are very uncommon. True? Well, in a way. The truth is that a mare conceiving twins is not entirely uncommon. What is rare, however, is the birth of two live foals. In fact, the odds of this occurring is estimated at about one in ten thousand. The odds of both or even one twin surviving are even slimmer. 

Twins occur when a mare releases two eggs. This is called ‘double ovulation’, and it can occur in as high as 20% of mares. Some mares are actually prone to double ovulation, and it is more common in draft breeds and thoroughbreds than in other breeds and ponies. Even if a mare releases two eggs, many factors play a part in whether these eggs are actually fertilised, and whether or not the mare is impregnated - with even one foal! Sometimes pregnancy may not even occur.

There are two kinds of ‘twin’ pregnancies - unilateral and bilateral. Unilateral means that both of the fertilised eggs are released on one side of the uterus. Bilateral means that there is one embryo on each side. Ultrasound technology can detect a pregnancy at as early as ten days, which is a great advantage in monitoring pregnancies for many reasons - including monitoring twin embryos. As the pregnancy progresses, ultrasounds can be used to detect the positions of the embryos, and can also be used to monitor their size and condition.

Many studies have been conducted of mares carrying twins, and in all cases, studies we have read agree that twins are rarely carried anywhere near close to term. This is where unilateral and bilateral pregnancies come into play. Unilateral twin pregnancies are more common than bilateral, however unilateral twins have a much lower chance of survival. They are both on the same side of the uterus, and by around day 40 of pregnancy, one embryo can abort and is re absorbed without any intervention. In most cases, nature seems to take care of the ‘problem’, allowing the surviving fetus the necessary space and nutrients. In some cases, both embryos will abort and be re absorbed.

In bilateral pregnancies, where two embryos are on opposite sides of the uterus, by day 40, it is more than likely that both embryos will have survived. However, as these pregnancies progress, both foetuses compete for space and nutrients from the mare, usually leaving one significantly weaker and smaller, even as the mare gets closer to foaling.

If allowed to progress, natural abortion of both twins is not uncommon - nor is the possibility of both foals being stillborn. Usually, in mid or late pregnancy, both foals are aborted and then expelled. This can have a variety of consequences for the mare, particularly if complications arise. Uterine scarring can occur, or the placenta may be retained, which can lead to serious infection and reduced fertility. This can also be life threatening.

Did you know?

Twinning is the number one cause of non-infectious abortions in mares.

If the twins are actually carried to term, this also places a risk on the life of the mare, and can make the birth very complicated and risky for all involved.

There are cases where both twins have survived, usually requiring care around the clock. Twins are generally smaller, weaker, less well developed, and in some cases have twisted or bent limbs. In the majority of cases, one or both twins will not survive. It may be harsh, but it is reality - a mare was not designed to carry more than one foal. So, what is the best course of action?  Well, that really depends on the time at which you discover that your mare is carrying twins. Most horses are scanned early on in pregnancy and this is mostly due to stud management procedure, as well as to comply with breeding agreements between mare and stallion owners. Some breeders who own both mares and stallions do not get their horses ultrasounded early on, but it is a good idea, particularly if you have a mare who has a history of double ovulation.

Unfortunately, it is a much better idea to ‘pinch’ an embryo if twins are detected early on. Ideally, this should be done before 16 days of pregnancy to avoid any complications. Your vet will be able to explain the procedure and discuss any risks with you at the time. Essentially, you are getting the vet to abort one of the embryos at this early stage in order for the other embryo to have a chance at life.

So, how does the vet choose which embryo to ‘pinch’? Usually, the embryo which appears less viable is the one that is aborted. There are conflicting views as to whether the smaller or larger embryo should be aborted. Some argue that reducing the larger will cause less irritation to the uterine walls, as they are said to be easier to abort - however - if the smaller embryo is already in the process of reducing, aborting and re absorbing naturally, then aborting the larger embryo may result in the loss of both foals. In any case, the positions of the two embryos has a great impact on which will be aborted. If they are too close together, or even in contact with one another, there is the option of aborting both embryos and re-breeding the mare. If one of the embryos has been pinched, a follow up ultrasound at day 28 is recommended to check the progress of the remaining embryo.

There is a common misconception that mares who are prone to double ovulation, or bearing twins should not be bred - however double ovulation actually gives the mare an advantage. If the mare is monitored carefully, it is estimated that 86% of the time, she will conceive - as opposed to a mare who only releases one egg - who has a 58% chance of conception. There is a high success rate in reducing twins to a single pregnancy in ‘double ovulation mares’ who are scanned before 16 days.

Even if twin foetuses are left until day 35, there are still options. Both can be aborted  at this time, or it may be possible for a vet to abort one embryo, depending on it’s positioning in the uterus and proximity to it’s twin. After 45 days, surgical removal of one fetus may be an option - or you can wait to see if one will abort and reabsorb naturally by itself, however you then risk the possibility of a mid to late term abortion of both foals, both foals being stillborn, or health complications with your mare - either from abortion, or the stress of foaling twins.

Do twin foals ever survive?

There have been many reported cases of live healthy twin foals born around the world. Most commonly, draft breeds seem to have the most success with twin foals, however there are even documented cases of ponies - even a miniature - giving birth to two healthy live babies! In some cases, the second twin is a complete surprise, with owners being totally oblivious to the fact that their mare carried twins all along! Even if both twins are alive at birth, one will be much weaker and smaller, and it is usually the smaller twin who does not survive, even with the best care and a co-operative mare.

Read the story of twin Warmblood foals, by none other than Joann Formosa's Paralympic Gold Medallist stallion, Worldwide PB, born at Tennyson Stud, NSW in 2011 (pictured - photo by: Claire Seidl).

TWIN FOALS – In the news around the globe

22 Year Old New Forest Mare Gives Birth To Twins - 2007

- St Leonards Farm, Beaulieu, UK

Two very healthy twin foals were born to ‘Royal Beatrice’, a twenty two year old bay New Forest Pony. The foals were a complete surprise to the pony’s owner, Stacey Gulliver, who was expecting just one foal! The twins have been named ‘Bess’ and ‘Royal’ - and they are both loudly coloured - thanks to their sire being an Appaloosa! ‘Bess’ is a brightly coloured strawberry roan, while ‘Royal’, the larger twin, is chestnut with a spotted blanket. The foals have been registered as first cross New Forest/Appaloosa ponies.

Twin Arabian Foals Born - Trouble and Surprise! - 2006

- Graham, Washington, USA

After two hours of labour, purebred Arabian mare ‘Scandalous Love’ had still not managed to give birth to her foal. In desperation, her owner, MiKael Caillier of Rising Rainbow Arabians, tried to pull the protruding foal leg free, while her vet, Jack Gillette, looked on. Luckily, the mare’s water broke, and the foal was born - but he’d already earned the name ‘Trouble’. However, Scandalous Love wasn’t finished yet. Arriving seven minutes after her brother, a filly was born - ‘Surprise’. Surprise didn’t have an easy start to life, and CPR had to be performed to keep the small foal breathing. A few months on, after a trip to the hospital for a swollen belly button and many sleepless nights, the foals were in good health and frolicking with their mother in the paddocks.

Twin Fillies Compete At Dublin Horse Show - 2007

- Dublin, Ireland

Two striking black fillies paraded around the arena with their dam, a ten year old grey Irish Draught Mare named ‘King’s Sister’. The fillies are both jet black, and were sired by the Thoroughbred stallion ‘Shaandar’. It was the first time twins have been exhibited at the Dublin Horse Show, and both twins definitely made an impression!

The World’s Oldest Horse Twins?

- Cardigan, Wales

At the ripe old age of twenty nine, horse twins Taff and Griff hold the Guinness World Record for being the oldest living horse twins. Julianne Aston from the society has remarked that the twin 11.2hh cremello ponies are so similar that a blue ribbon must be tied in the mane of one of the ponies just so people can tell them apart!

Special Delivery at Rhythm Sporthorses - 2004

 - Mokau, New Zealand

Early on Friday 19th of November 2004, ‘Laurrel’,  a mare at Rhythm Sporthorses began to give birth. Her owner, Lynley Bolt, looked on as Laurrel gave birth to a little bay filly. The mare was still restless, and soon after, a bay colt was born! A vet was called to attend, and as the mare hadn’t yet expelled the afterbirth, there was much work to be done! With much love and care, after veterinary attention, milking the mare and finding makeshift rugs for the foals, things began to improve. By that evening the foals were standing. Nine years on, and ‘Rhythmic Lakota’ and ‘Rhythmic Skywalker’ are both strong and healthy young horses!

Thank you to The Stable Magazine for this article, which was originally published in their January 2014 issue. Check out The Stable Magazine online now for FREE. Read this article and many more at www.thestablemagazine.com