Reproduction

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

Q: How long is a mare's estrous cycle?

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

Q: How long is a mare in heat?

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

Q: When is foal heat?

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

Updated 1 Nov 20263 sources

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].

Related tools and references

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References

Features of the Reproductive Cycle (table)MSD Veterinary Manual
Approximate Gestation Periods (table)MSD Veterinary Manual
Understanding Reproductive Events in the Mare for Successful Breeding Programs (Bulletin 1434)Bohlen J — University of Georgia Cooperative Extension · 2014, reviewed 2024

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