Pregnancy in the mare – health and well-being

As with human pregnancy, the first few days are the most critical. During the first month, there is a 10-15% chance that the embryo will be resorbed. Early embryonic loss can be caused by the following problems:

  • stress
  • illness
  • uterine infection
  • hormonal abnormalities
  • twins

Following conception, the pregnancy can be confirmed by ultrasound or transrectal palpation at approximately 30-35 days. It is wise to have this re-confirmed at 45, 60 or 90 days.
From here on in, regular deworming, vaccinations, exercise and a balanced dietwill help ensure a healthy pregnancy and successful birth.

Most people have pre-conceived ideas about how delicate and fragile a pregnant mare can be. Well... in a natural setting the mare does comparatively well reproductively considering how relatively poor a mare's reproductive performance is compared to other domestic animals. Good management is essential, but being over-protective is not necessary!

Good brood mare management is essential for a successful pregnancy. Your mare should be fit and possibly gaining weight. Avoid stress as this can cause a decrease in progesterone which helps maintain pregnancy. Illness and/or fever can cause the mare’s system to secrete prostaglandins which may cause abortion.

The do’s and don’t’s:



  • transport your mare unless essential
  • administer hormones or other drugs unless prescribed by your vet
  • expose your mare to other horses if there is a risk of illness or injury
  • expose your mare to unnecessary or undue stress

During the first 7 months of pregnancy you can treat your horse as you would normally, unless there are circumstances that do not allow this, e.g. malnourished mare, obese mare, etc.


The weather should be taken into account as this could have an impact on amounts fed. She should have a continuous supply of clean, fresh water and her feed should include a high quality forage. During the first 7 months of pregnancy you should feed your mare as you have been doing previously, a balanced and healthy diet for her size and temperament.
During the last 4 months of pregnancy the foal will start to grow rapidly. To accommodate this, the mare’s energy requirements will increase by up to 50% – good quality hay and forage should remain the main source of this energy, it isn’t necessary to feed special nutritional supplements. Concentrated feeds, e.g. grains, may need to be added to the feed to boost energy levels without adding excessive amounts of bulk.
Be sure your mare does not become obese – this will only become a disadvantage to her.


Your mare should be kept up-to-date with her course of vaccinations against tetanus and flu. This is important as infectious diseases can trigger abortion. It is good practice for your mare to have a booster vaccination 4 weeks before foaling, the concentration of antibodies to these infections in the first milk (colostrums) will be significantly increased and the foal will obtain immediate protection as soon as it suckles.
It is also advisable to have your mare vaccinated against Equine herpesvirus (EHV) at the 5th, 7th and 9th months of pregnancy. If a mare is affected by EHV she may abort in late pregnancy or give birth to a weak foal that may die in the first few days of life.
Some studs also recommend vaccination against Rotavirus at the 8th, 9th and 10th month of pregnancy. If a foal is affected by Rotavirus, it will cause diarrhoea with high mortality rates seen in foals under 3 months. However, if the mare is vaccinated the foal will be provided with immunity via the mare’s milk.


Generally, pregnant mares are dewormed routinely as per the active ingredients’ recommended dosing interval. Most wormers available today are safe for pregnant mares, it is, however, wise to consult your vet to establish an effective and safe deworming regimen for her.
In late pregnancy a mare’s natural resistance to worms is lowered, so it is even more important that she is wormed at this time as she will be the primary source for infecting her foal with parasites.

Foot and dental care

Most brood mares are left unshod, which means that regular trimming at 6-8 weeks is important to prevent foot abscesses which are common in mares with overgrown feet.
Dental care is also very important. Your mare should have her teeth checked at least once a year, if not twice yearly. She will be able to utilise her feed with maximum efficiency and without discomfort. It is advisable to have her teeth checked at the time of the 1st pregnancy check.

In horses the average pregnancy (gestation period) is 342 days (approximately 11 months), but can range from 321-365 days. Prolonged gestation is not generally a problem, but if you are concerned, ask your vet to examine your mare to determine if she is still pregnant and confirm that all is going well.
Continuing exercise is essential. Mares can be ridden lightly for the first 4-5 months of pregnancy, after then a pastured mare will get as much exercise as she needs while grazing. Regular paddock exercise in late pregnancy is essential. Vigorous exercise, however, is not recommended at any stage of pregnancy.
Mares do occasionally abort. If you notice any vaginal discharge or dripping milk during pregnancy, call your vet. If you find remains of a placenta or foetus, put it to one side for your vet to examine – it may be possible to find out the cause of abortion and treat the mare accordingly. Mares can abort without ill-effects, however, you should always have your mare examined by a vet just in case there are complications, eg retained placenta, which can be life-threatening.