Getting a mare ready to breed starts in autumn: check her body condition (aim for about 3.5 out of 5), vaccinations, deworming, teeth and feet. For early breeding, put her under lights from 1 December, 16 hours a day. A reproductive examination by your vet completes the preparation.
When should you start preparing a mare for breeding?
In October or November, because the mare is a seasonal breeder. She cycles roughly every 21 days, but only when days are long. According to the French Horse and Riding Institute (IFCE) presentation on breeding mares, autumn is a period without ovulation, winter is complete rest (anoestrus), and spring is a transition with long, often misleading heats. The ideal period runs from May to July.
Left to nature, a mare usually does not ovulate for the first time until mid-April or May (Colorado State University). If you want to breed in February or March, the decisions are made before winter: choice of stallion and breeding method, getting the mare into condition, and a lighting programme.
What does the ideal broodmare look like?
The same IFCE presentation sums up the factors that affect fertility. A good candidate is:
- in good general health, with no ongoing condition (laminitis, asthma, ulcers, Cushing's disease…);
- ideally between 4 and 12 years old;
- in sound body condition, around 3.5 out of 5;
- comfortable on all four legs;
- with good teeth;
- up to date with tetanus, flu and EHV (rhinopneumonitis) vaccinations;
- dewormed regularly;
- with good vulval conformation.
An older mare can still be bred: just ask your vet to examine her earlier.
How do you put a mare under lights?
You artificially lengthen her days from 1 December so that her body thinks spring has come. According to the IFCE, it is the only way to bring her breeding season forward. Day length works through melatonin, a hormone produced at night: as nights get shorter, the mare restarts her ovarian activity. Allow about 60 to 70 days from the start of lighting to the first ovulation, which means a mare ready from February.
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Start on 1 December
Begin during the short days, about 60 to 70 days before the date you want to breed.
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Aim for 16 hours of light a day
Natural and artificial light combined: about 16 hours of light and 8 hours of darkness. Leaving the lights on 24 hours a day brings no benefit and may even work less well.
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Keep the light bright enough at eye level
About 100 lux at the level of the mare's eyes, checked with a light meter. Keep natural daylight too: the mare should still see the day.
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Automate it with a timer
A timer switches the stable light on at dusk and off around 11 p.m., every day, with no gaps. A light mask worn in the field (such as Equilume®) is an alternative.
Not every mare is suitable. The IFCE advises against lighting thin mares (body condition score of 2 or less) and fillies under 2 years old. It is useful, on the other hand, for older mares and for mares with a history of early embryonic loss. Expect the mare to shed her winter coat earlier too: plan a rug if she goes out.
What body condition should a mare have before breeding?
Neither too fat nor too thin: a body condition score of around 3.5 out of 5. Poor nutrition is one of the main causes of infertility (IFCE). A thin mare must gain condition before going under lights, which is why the check happens in autumn.
- Too little protein or energy: lower reproductive performance.
- Too much protein: strain on the body.
- Minerals, trace elements and vitamins: the mare's immunity, then the foal's muscle and joint health.
Some breeders use flushing: a slightly increased ration, raised moderately and gradually until covering. Every change of feed should be gradual; have the ration checked by your vet or an equine nutritionist.
Which vaccines and deworming before breeding?
The mare should be up to date against tetanus, equine flu and EHV (rhinopneumonitis). Check this in the month before she goes to the stud or breeding centre, where mares mix. Some breed registries require it: in France, for example, the IFCE lists flu for the Selle Français and flu plus EHV for the French Trotter and the Thoroughbred. Breeding centres often require it too. Rules differ by country and studbook, so check yours. For booster timing, read our article on horse vaccines in autumn.
For deworming, the IFCE recommends a treatment against strongyles and tapeworms in late autumn, with 1 to 3 dewormers a year depending on the parasite risk on your farm and faecal egg count results.
Which vet checks are needed before breeding?
A general examination and a reproductive examination, external and internal, by your vet. They check the vulval conformation and the reproductive tract, and can follow the follicles by ultrasound to predict ovulation.
Depending on the breed and breeding method, screening tests may be required. In France, the IFCE lists:
| Disease | Mares concerned |
|---|---|
| Contagious equine metritis (CEM) | Mares covered naturally early in the breeding season, or when changing stallion |
| Equine viral arteritis (EVA) | Mares covered naturally, or inseminated at a centre housing stallions, within the 30 days before breeding |
| Both tests above | Compulsory for mares bred to a Thoroughbred stallion |
Outside France, ask your national studbook or breed society and the stud, which often has its own requirements.
Timeline for breeding in February or March
| When | What to do |
|---|---|
| October – November | Decide to breed, choose the stallion and breeding method, score body condition and adjust the ration |
| Late autumn | Deworm for strongyles and tapeworms (based on faecal egg counts), check teeth and feet |
| 1 December | Start the lighting programme: 16 hours of light a day, about 100 lux |
| December – January | Check vaccinations, reproductive examination, screening required by the studbook or stud |
| February – March | First ovulations expected (60 to 70 days after lights on), ultrasound follow-up and covering |
How to keep track of it all easily
Lights-on date, vaccines to check, deworming, scans: with several mares, the dates soon overlap. In EquiFarmX, each mare has her own breeding calendar (heats, scans, coverings, pregnancy) and every treatment has its reminder. Your vet can see the record without installing anything. Details are on the features page.
Frequently asked questions
When should I put my mare under lights?
Around 1 December for a mare to be bred from February (Northern Hemisphere). Allow about 60 to 70 days from the start of lighting to the first ovulation.
How many hours of light does a mare need?
About 16 hours of light a day, natural and artificial combined, and 8 hours of darkness, at roughly 100 lux at eye level. Lighting 24 hours a day is unnecessary.
Can a thin mare be put under lights?
No. The IFCE advises against it below a body condition score of 2. The mare should gain condition first, on a ration approved by your vet.
Should a pregnant mare be put under lights?
Only if she is due to foal in January, February or early March and you want to rebreed her soon after foaling, according to Colorado State University. For mares due in April, May or June, it is not needed.
What is the best age to breed a mare?
Between 4 and 12 years old is ideal according to the IFCE. An older mare can be bred after a vet examination; lighting often helps her.
Sources
- IFCE — Mise à la reproduction de ma jument : comment faire ? (Dr Charlotte Degien, with Dr Marie Delerue, IFCE, 10/10/2023, in French)
- IFCE Équipédia — La mise sous lumière ou photostimulation (in French)
- IFCE Équipédia — Bien préparer sa jument pour la mise à la reproduction (in French)
- Colorado State University, Equine Reproduction Laboratory — Putting a mare under lights (2022)