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How Long Are Horses Pregnant? A Comprehensive Guide to Horse Pregnancy

Aside from knowing how long your horse will be pregnant for, there is considerably more you should know about if you’re considering breeding your horse and having a safe and healthy pregnancy. 

First, how long are horses pregnant for in months? In short, horses are pregnant for 10 to 12 months, and most mares only carry one foal per pregnancy – however, although rare, twins do sometimes appear. 

How many days are horses pregnant for, though? For a more specific answer on a horse’s gestation period, horses typically tend to be pregnant for 326 days to 354 days, however, there are cases where prolonged gestation has lasted as long as nearly 370 days. 

Did you know that horses are seasonally polyestrous? This means that your mare has a fertility season similar to that of a cat in that she will experience several cycles during a particular season – with their cycle being during periods of longer daylight length. This cycling pattern is thought to be an evolutionary development that ensures the mare will give birth at the most hospitable time of the year, spring. 

Because of this, and the length a horse is pregnant for, a mare can typically only go through one pregnancy per year, resulting in one foal in a given year.

How Long are Miniature Horses Pregnant?

Similarly to how long other horses are pregnant, miniature horses and all other breeds of female horses will typically carry their foals for approximately 11 months. The average miniature mare will carry her foal for around 330 days before she gives birth – with the actual length of pregnancy lasting from 320 days to 380 days.

Understanding the Cycle of a Mare

A good understanding of a mare’s cycle is key when it comes to the management of your mare in general – and it is absolutely essential when planning to successfully breed. As mares are seasonally polyestrous, the mare will be light responsive, resulting in a start of her cycles caused by a decrease in melatonin from increasing daylight hours. 

Some important dates for horse breeders to remember are: 

  • The Summer solstice – the longest day of the year and the peak of the natural breeding season.
  • The autumn equinox – where there is equal light to dark in the day and where the mares are turning off in autumnal transition.
  • The Winter solstice – the shortest day of the year where mares will be in deepest anestrus.
  • Spring equinox – another time of equal light to dark in the day, but the mare will be in a springtime transition. 

The dates for the above do change per year, so please research when the date will be for the year you wish to begin breeding your mare. Additionally, the temperature can influence the onset of cyclicity as this is most likely to be partly regulated by a neurotransmitter which is involved in the secretion of prolactin. It is also widely thought that the reduction of opioid inhibition from the gonadal axis can also trigger the beginning of the mare’s breeding season. 

Finally, the mare’s gestation period can also be impacted by seasonal effects – with mares that were bred in the first quarter of the year often carrying their foal for slightly longer than expected, and mares bred during seasons of longer days may have a slightly shorter gestation period.

Some other factors that can affect how long a horse is a pregnant include whether the foal is a colt or a filly – with the period for colts being up to seven days longer than fillies. Body weight can also affect how long horses are pregnant, as thinner mares tend to carry their foals longer than those with more weight. 

How Long are Horses Pregnant? 6, 7, and 9-Month Pregnant Horses Explained

Horses in Summer

Pregnant mares will go through three trimesters with the first beginning at conception and being confirmed at around two weeks. During the first trimester, it is essential that the mare is examined by a veterinarian in order to make sure she and her foal are in good health. 

At around 25 days, the veterinarian will be able to perform an ultrasound which can detect the heartbeat of the foal and confirm its vitality. It is also during this period in which twins can be confirmed. If a mare is found to have twins, the veterinarian may ask if the owner wishes to terminate the second embryo to give the mare and the remaining embryo a better chance of survival. 

Horses that are 3 months pregnant will have ultrasound examinations that show what looks like a horse – with key features and the gender being identifiable. 

A 6-month pregnant horse will begin to show that they are pregnant, with the second-trimester beginning at day 114. During this time, the mare is able to receive dewormer and vaccinations. The mare should also have an increase in feed to provide nutrition for the goal. 

A horse 7 months pregnant, and in her third trimester at 226 days, will require more frequent vet visits – with regular exercise needing to be stopped from the seventh month. A horse 9 months pregnant will be near to giving birth and, as your mare nears giving birth, she must be kept in a comfortable and stress-free environment. 

Leading up to Birth – 11-Month Pregnant Horses

An 11-month pregnant horse will be very near to foaling day, and this can happen anywhere between day 326 and day 354 on average. There are also some test kits some breeders use that help to anticipate the due date, and these can be useful on the mare’s first birth as their foaling process will be unknown. 

In the days leading up to delivery, the mare’s body will be showing signs that she is ready to give birth. This can include a full-looking udder, dripping milk, and a low-hanging belly. 

During the near-birthing period, the mare should be provided plenty of fresh straw and hay to provide enough comfort. As she goes into labour, she will also likely paw at the ground and appear restless, but she will give birth lying down. 

Typically, the first thing to be visible during the birthing process is the amniotic sac, followed by the head and the legs of the foal itself. Once the amniotic sac is visible, the foal will typically be born within a few minutes. 

Labour and Delivery – What You Should Know

Interestingly, most mares give birth at night – possibly a survival adaptation which allows the foal and mother to be ready to run once daylight arrives. 

During the beginning stages of labour, the mare will be anxious – possibly kicking at her belly and adopting nesting behaviour. Many mares also sweat during the foaling process, often referred to as the mare “heating up”. During this hour-long period, wrap her tail and clean the perineal area. 

The second stage of labour is much shorter, typically lasting up to 25 minutes. Continuous progress through your mare’s labour should reveal the foal’s front hooves, nose, and ears. 

Normally, a veterinarian will be in attendance to determine that the foal is breathing after birth – this may need to be stimulated with the use of a blunt object lightly massaging the foal’s nostrils or rubbed vigorously with a towel if they are still not breathing. 

Further tips for the birth of a foal include the disinfecting of any showing biologicals with iodine. It is also advised that the umbilical cord should not be cut immediately as it is believed that a certain amount of blood still flows into the goal after birth through the umbilical artery. 

In the third stage of labour, after the foal has been born, you’ll be waiting for the placenta to pass. If the placenta has not passed within three hours, it should be considered an emergency in which a vet should be contacted. 

The foal should be standing within an hour after birth and should also demonstrate the ability to nurse within two hours. The mare herself should usually require no post-partum care.

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If you found this article on horse pregnancy educational and want to learn more, contact the friendly and knowledgeable team at Prime Stables through our handy online form. We are always happy to offer our expertise to support horse owners during this exciting time.

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