The Reproductive Cycle

Type of breeder:  Polyoestrus
Natural Season:  Spring and Summer - long daylight hours.
Oestrus cycle:  21 days long with oestrus ranging from 2-8 days.
Gestation period:  11 months

Preparation For The Mare Prior To Breeding

Breeding from the mare is an important decision and careful thought should be put in before starting any breeding program. The mares confirmation, age and suitability as a dam should be carefully considered first, before then deciding on the foals proposed use, size and time of year to be born. Finally, the stallion required to produce such a foal and pass on certain traits should be chosen. The stallion chosen often dictates whether breeding will be via Artificial Insemination (A.I.) or covering mares naturally by walking them in.

The mare should ideally under go a pre-breeding exam, to confirm her breeding history and ensure that her ovaries are active and cycling regularly. The uterus and cervix are also checked for any anatomical abnormalities that may prevent a fetus being carried to term or for infection or trauma caused by previous foalings. Many studs now ask for swabs to check the mare is free of Contagious Equine Metritis and blood tests for Equine Viral Arteritis and Equine Infectious Anaemia and possibly Strangles, prior to breeding.

Pregnancy Diagnosis

After the mare has been inseminated or covered, a first scan can be made on day 2-3, to ensure ovulation has occurred and a good corpus luteum is present in its place. At this point it is too early to detect an embryo, but it does show whether or not ovulation has happened. Pregnancy diagnosis is then made on day 14-16 when the mare is also checked for twins. Due to the stresses put on both the mare and the developing foals, it is advisable not to allow both twins to reach full term. If your mare has conceived twins, then your vet will advise you of the best course of action, for both the mare and foals. If scanned as not in foal at this stage, then the mare can be covered on the next cycle, as long as her ovaries are cycling correctly. Scanning again at 25-30 days confirms the fetus has attached onto the uterus and that a heartbeat is present. Further scans can be done at 40 to 60 days to assess normal fetal development and then again in the Autumn – around October to check the mare is still in foal going into the Winter.

Worming During Pregnancy

It is important to maintain worm control during pregnancy, but worming products must be licensed for use in pregnant mares. Worm faecal egg counts are the most effective way of deciding which worms are currently a problem in the mare and your vet will be able to advise on which products are safe to use and when during gestation. It is best however, to avoid worming in the first trimester of pregnancy or in the last month of gestation.


It is important to maintain a vaccination program throughout. Annual boosters for Flu and Tetanus should be performed in the 4-6 weeks before foaling, to guarantee the mares colostrum contains adequate antibodies, to pass onto the foal for the initial 6 weeks. Equine Herpes vaccinations should also be started during gestation as the virus can cause abortion in the last trimester. Vaccinations should be given during the 5th, 7th and 9th month of gestation.

Post – Foaling

Retained placenta

The placenta should be passed within 20 minutes of foaling down. However if after two to three hours the placenta is still attached to the mare, then the vet should be called to remove it. Leaving it in for longer can cause a septicaemia to set in, which can become fatal to the mare if left untreated.

Anti tetanus

Prior to foaling, the mare should be up to date with her influenza and tetanus vaccinations and should have had a further vaccination in the last month of gestation. This helps ensure antibodies against tetanus are passed onto the foal once born, however the immunity can be additionally boosted again, by giving the foal an injection of tetanus antitoxin. This provides additional cover for 6 weeks and is advisable.


Colostrum may not be passed onto the foal for many reasons, including low milk production, loss of colostrum prior to foaling or inability of the foal to suckle. The amount ingested, may not contain an adequate amount of antibodies, causing problems later on. A blood test taken at least 24 hours after birth, can check the level of antibodies present. If they are low, then further treatment may be needed.

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