# Mare Reproduction: Breeding Season, Estrous Cycle, Ovulation & Foal Heat

> Reproductive physiology of the mare: long-day seasonal breeder, 21-day cycle (19–23), estrus 5–7 days, ovulation 1–2 days before the end of estrus, foal heat at 9 days (4–14), double ovulation about 20% — cited.

- Source page: https://wevet.in/reproduction/horse/
- Type: Reproduction
- Publisher: WeVet
- Updated: 2026-11-01
- Audience: veterinarians and veterinary students

Key reproductive figures for the mare from the MSD Veterinary Manual [1][2] and from University of Georgia Cooperative Extension [3].

## Key figures

| Feature | Horse | Source |
|---|---|---|
| Age at puberty | 10–24 months | [1] |
| Cycle | Seasonally polyestrous, early spring through summer; approx. 21 days (19–23) | [1] |
| Duration of estrus | 5–7 days | [1] |
| Ovulation | Usually 1–2 days before the end of estrus | [1] |
| Best time to breed | Last few days of estrus, just before ovulation; bred at 2-day intervals | [1] |
| First estrus after foaling | 9 days (4–14) | [1] |
| Gestation | 11 months | [2] |

Double ovulation occurs in approximately 20% of estrous periods, but twins rarely progress to term [1].

## The mare's cycle

- The seasonality of the mare's breeding cycle is mostly dictated by photoperiod; mares are long-day breeders [3].
- The estrous cycle is approximately 21 days, give or take 3 days, and each mare is fairly consistent in her own cycle length [3].
- Estrus normally lasts 5 to 7 days but can be as short as 2 or as long as 12 days [3].
- The luteal phase controls the largest portion of the cycle, with approximately 14 days dedicated to the corpus luteum [3].
- Ovulation generally occurs 0–48 hours before the end of estrus [3].
- A producer can usually identify the phase a mare is in by teasing with a stallion; some mares show silent heat, for example with a foal at side or with improper body condition [3].
- The corpus luteum supports the pregnancy until approximately 120–150 days of gestation [3].

## Frequently asked questions

### How long is a mare's estrous cycle?

Approximately 21 days (19–23) [1]; University of Georgia Extension gives approximately 21 days, give or take 3 days [3].

### How long is a mare in heat?

5–7 days [1], although estrus can be as short as 2 or as long as 12 days [3].

### When is foal heat?

The first estrus after parturition occurs at 9 days (4–14) [1].

## References

[1] Features of the Reproductive Cycle (table) — MSD Veterinary Manual. https://www.msdvetmanual.com/multimedia/table/features-of-the-reproductive-cycle
[2] Approximate Gestation Periods (table) — MSD Veterinary Manual. https://www.msdvetmanual.com/multimedia/table/approximate-gestation-periods
[3] Understanding Reproductive Events in the Mare for Successful Breeding Programs (Bulletin 1434) — Bohlen J — University of Georgia Cooperative Extension (2014, reviewed 2024). https://fieldreport.caes.uga.edu/publications/B1434/

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Numbers in [brackets] cite the references above. For veterinary professionals. Information supports — never replaces — clinical judgement; always check the current product label and local regulations.
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