Breeding from your mare – what to consider!

Most of us who have owned a mare have, at some point, thought about putting her in foal. Breeding your own horse can be incredibly rewarding but it is important to give careful thought to what will actually be required! It is not something to be undertaken lightly to say the least.

Take the time to think about the following questions:

  1. Is the mare registered with a breed society or of known breeding?
  2. Has the mare had a successful competition career?
  3. Is she healthy and sound? Does she have good conformation?
  4. Does she have a good temperament?
  5. How old is she? (Fertility declines as the mare gets older.)
  6. HOW MUCH ARE YOU WILLING TO SPEND? (We cannot stress enough how important it is to decide on a budget before embarking on breeding your mare – we cannot guarantee success and the costs can mount up considerably in a short space of time!)

More than anything else, the lifelong welfare of the mare (and potential foal) should guide any decisions.

If you aren’t discouraged by what you’ve already read then we will start to think about getting the mare ready to breed!

Mares usually have a 21 day oestrus cycle. This is divided into oestrus or ‘in season’ (lasting 5-7 days) and dioestrus (14-16 days). During oestrus the mare will develop one or more follicles within the ovaries which will ovulate. Ovulation usually occurs approx 24 hours before the end of oestrus.

Mares are seasonal breeders and are influenced by factors such as daylight and temperature. Mares are usually anoestrus (not cycling) in Winter and then enter a ‘transitional period’ as they begin cycling in the Spring. However, up to 30% of mares will cycle all year round!

The gestation length of mares is 340 days (11 months) but can vary between 320-360 days.

Pre-breeding examination

Your vet will perform a thorough clinical examination of your mare to assess her general health. This will be followed by a gynaecological examination. This includes a visual examination of the vulva, vagina and cervix, and rectal palpation/ultrasonography of the uterus and ovaries.

Clitoral swabs are taken for CEM, Klebsiella pneumoniae and Pseudomonas aeroginosa (after January 1st of the current year). An endometrial swab can also be taken for culture and cytology.

Many studs/breeders/AI centres will require testing for a number of other diseases prior to breeding. These include blood tests for Equine Viral Arteritis Virus (EVA), Equine Infectious Anaemia (EIA) and Strangles.  Mares should also have up to date vaccinations for Influenza and Tetanus. You should also be aware that it is recommended for mares to be vaccinated against Equine Herpes Virus (a major cause of abortion) in the 5th, 7th and 9th month of gestation.

Natural Covering or Artificial Insemination

Natural covering may be an option if the stallion is local to you. The stallion may be left with the mare or led to her whilst she is in season. Natural covering can be very dangerous.

Many owners will now choose artificial insemination for their mares. This will require closer monitoring of the mare to assess when she is in season. Some mares will show very obvious signs of oestrus but many will not. Mares can be assessed by rectal ultrasonography of the uterus and ovaries to decide the optimal time for insemination. Certain drugs can also be used to manipulate the mare’s oestrus cycle.

Artificial insemination can be performed using fresh, chilled or frozen semen. Fresh semen is only an option if the stallion is very local to your mare. Chilled semen is widely available and tends to have higher conception rates than frozen semen. Frozen AI also requires more frequent scanning of the mare as she will need to be inseminated within 6 hours of ovulation.


Some mares may react to the semen 24-48 hours after insemination. We can detect this by scanning the mare following insemination to check for inflammatory fluid, which we can then flush away using sterile fluids.

The first pregnancy scan can be performed 14-15 days after ovulation when we will also check for twins.  Further scans can be performed at later dates to check for a heart beat etc.

We have seen some lovely foals already this season and will undoubtedly see a few more in the coming months!


If you would like to speak to one of us about breeding your mare then please get in touch on 01296 621 840. We are always happy to discuss individual cases with owners.






One thought on “Breeding from your mare – what to consider!

  1. Pingback: Breeding from your mare - what to consider! - Wendover Heights Veterinary Centre Wendover Heights Veterinary Centre

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