A mare is an adult female horse, typically defined as three years of age and older. The term applies to horses, donkeys, and other equines. In everyday equestrian use, “mare” is the standard way to refer to any adult female horse, whether she is in active work, breeding, retirement, or any other stage of life. Understanding the characteristics, behaviour, and management of mares is fundamental to working with horses at any level.
Mare vs Filly vs Broodmare
Female horse terminology varies by age and purpose:
- Filly — a young female horse, typically under three years of age (though some breed registries and racing contexts use four years as the threshold).
- Mare — an adult female horse, three years and older.
- Broodmare — a mare used specifically for breeding. A well-bred broodmare from a successful performance line can be worth considerably more than her competition career alone would suggest.
- Dam — a mare in relation to her offspring; the mother of a foal.
Mare Behaviour and the Oestrous Cycle
Mares are seasonally polyoestrous — they cycle through periods of reproductive activity during spring and summer, with reduced activity or full anoestrus (no cycling) through the shorter days of autumn and winter. During the breeding season, the oestrous cycle lasts approximately 21 days, with oestrus (the receptive “in season” period) lasting 5–7 days and dioestrus (the non-receptive phase) lasting around 14–16 days.
Behavioural changes associated with oestrus can be pronounced in some mares and barely noticeable in others. Typical signs include:
- Increased sensitivity along the flanks and hindquarters
- Raised tail, frequent urination, and “winking” (repeated opening and closing of the vulva)
- Restlessness or changes in temperament, including increased distractibility
- Changes in response to other horses — increased interest in geldings or stallions, or in some cases, aggression toward other mares
The impact on performance work varies widely. Many competition mares work through their seasons without issue; others show a marked deterioration in concentration, willingness, or comfort. A veterinarian can discuss hormonal management options for competition mares where cycles significantly affect performance — Regumate (altrenogest) is the most commonly used product under veterinary prescription for this purpose.
Mares in Performance
Mares are well represented at the highest levels of equestrian sport. Some of the most celebrated horses in racing and dressage history have been mares — they are no less talented or athletic than their male counterparts. Individual mare characteristics vary enormously: some are straightforward, honest workhorses; others are sensitive, opinionated, and require a thoughtful rider who earns their respect rather than demanding compliance. Experienced horsemen often describe mares as “when they give it to you, they really give it” — meaning that a mare who trusts and respects her rider will work with total commitment.
Breed characteristics also influence mare temperament significantly. Arabian mares are known for sensitivity and intelligence; Thoroughbred mares for athleticism and sometimes heightened reactivity; draught mares for reliability and equable temperament. Individual variation within breeds is always more significant than breed generalisations.
Reproductive Life of a Mare
Mares typically begin cycling in earnest from around two years of age, though breeding before three or four years is generally considered too early for the mare’s physical development. A mare can continue to conceive and carry foals well into her late teens or early twenties, though fertility declines with age and pregnancy in older mares carries increased risk. A mare’s gestation period is approximately 340 days (just over 11 months).
In the days following birth, a mare exhibits strong maternal instincts — bonding with her foal rapidly through smell, touch, and vocalisation. The first hours after foaling are critical: the foal must stand and nurse within the first two hours to receive the protective colostrum, and the mare’s acceptance of the foal should be monitored closely, as some maiden mares (those foaling for the first time) may initially reject or be nervous around their foal.
A mare can come back into oestrus as early as 7–10 days after foaling — the “foal heat” — though most breeders choose not to breed on foal heat due to slightly lower conception rates and the mare’s still-recovering uterus.
Frequently Asked Questions
Are mares more difficult to ride than geldings?
This is one of the most frequently debated topics in equestrian circles, and the honest answer is: it depends entirely on the individual horse. Some mares are exceptionally straightforward, generous, and easy to work with. Others are more complex, requiring a sensitive, consistent rider who earns their trust rather than demanding submission. Geldings tend to have more consistent behaviour day-to-day because they lack a hormonal cycle, but a “difficult” gelding can be every bit as challenging as a cycling mare. The quality of the horse’s training, its early handling, and the rider’s skill and approach matter far more than whether the horse is a mare or gelding.
How do I know if my mare is in season?
The clearest signs are behavioural: raised tail, frequent urination, winking of the vulva, restlessness, and — if other horses are nearby — an obvious interest in or receptiveness toward them. Some mares also become more sensitive to grooming along the flanks and hindquarters when in season, and their response under saddle may change (increased distractibility, unwillingness to engage the hindquarters, or a general “not quite herself” quality). If you are unsure whether hormonal cycles are affecting your mare’s behaviour or performance, your vet can assess her cycle via rectal ultrasound and discuss management options.
What is a maiden mare?
A maiden mare is a mare that has never been pregnant. In breeding contexts, maiden mares can be slightly more unpredictable around foaling and in early motherhood because they have no previous experience. They may be nervous, overprotective, or, in rare cases, initially rejecting of the foal. Having an experienced stud hand present at foaling and for the first hours afterward is particularly important with maiden mares. In racing, “maiden” refers to a horse (of either sex) that has not yet won a race — a separate use of the term.