One of the most common questions horse breeders ask, or are asked, is: "How old is too old to breed a mare?"
The simple answer is that there is no simple answer. There is no universal retirement age for broodmares, just as there is no universal retirement age for riding horses. Some horses seem to enjoy being ridden right up to the end, while others need to retire in their teens. Some mares successfully produce healthy foals into their early or even mid-twenties, while others may experience declining fertility or pregnancy complications much earlier.
Rather than focusing on a specific birthday, veterinarians and horse breeders evaluate each mare individually, taking into account her overall health, reproductive history, and the condition of her reproductive tract.
Age is only one part of the picture
Although age is an important factor in broodmare fertility, it should never be considered in isolation.
Veterinarians generally assess:
- Overall health and body condition
- Previous foaling history
- Fertility history
- Uterine health
- Cervical function
- Perineal conformation
- Presence of reproductive disease
- Ability to carry a pregnancy safely
A healthy mare with a long history of successful pregnancies often has a better outlook than a younger mare with significant reproductive problems.
When does fertility begin to decline?
Most mares reach their peak reproductive years between approximately six and ten years of age.
From around 15 years of age, fertility gradually begins to decline. Older mares may:
- Take longer to conceive
- Have lower conception rates
- Experience more early pregnancy loss
- Develop uterine changes that reduce fertility
- Be more prone to uterine inflammation after breeding
These changes occur gradually and vary considerably between individuals. Many mares continue to produce healthy foals despite this natural decline in fertility.
Can a 20-year-old mare still have a foal?
Yes.
Many mares successfully carry healthy foals into their twenties. This is more true if the mare has had previous foals. As our next section highlights, you would not want to breed a 20-year-old mare for the first time.
Vets usually recommend closer reproductive monitoring as mares reach 20 years of age, because the risks associated with pregnancy begin to increase. Some practitioners advise discussing alternatives such as embryo transfer for valuable mares once they reach approximately 20 to 21 years of age, although many healthy mares continue to carry pregnancies successfully beyond this age.
Older maiden mares
An older maiden mare — a mare being bred for the first time later in life — often presents different challenges from an older mare that has produced foals throughout her breeding career.
As mares age, the reproductive tract becomes less elastic, the cervix may not relax as effectively, and uterine clearance after breeding may become less efficient. These factors can make conception and pregnancy more difficult for older maiden mares. While there are treatments for the tight cervix associated with older maidens that can be tried, they require a lot of special attention and have mixed degrees of success.
A "tight cervix" (more accurately, poor cervical relaxation) is one of the more common reproductive challenges in older maiden mares and mares that have not foaled for many years. The cervix doesn't dilate and drain uterine fluid as efficiently, making these mares more susceptible to post-breeding endometritis. This means the embryo cannot survive in the uterus and the mare will not get pregnant.
Does breeding every year help?
Many breeders wonder whether mares should have a foal every year or be given regular years off.
Current veterinary opinion suggests that, provided a mare remains healthy and maintains good body condition, breeding annually does not reduce the quality of future foals. In fact, many mares cycle more consistently when they produce a foal each year. Decisions about giving a mare a breeding break should be based on her health, reproductive history, and management needs rather than the assumption that every mare requires regular years off.
There seems to be a fair amount of clinical opinion among repro vets that breeding every year may be helpful for fertility. Dr. Katherine Joos (AAEP), writing for the American Quarter Horse Association, states:
As long as a mare is able to maintain a healthy weight while nursing a foal, I find no reason not to breed her back year after year.
She also notes that breeding every other year does not improve the quality of the foal produced. Dr. Joos also states:
In my experience, mares tend to cycle more consistently and normally when bred every year.
She goes on to recommend annual breeding for healthy mares, and also suggests that embryo donor mares should periodically carry a pregnancy because it helps maintain normal cervical function.
The proposed reasons that many repro vets fall on the side of allowing a donor mare to carry a foal to term every couple of years include:
- better cervical relaxation
- maintenance of cervical elasticity
- improved uterine clearance
- fewer chronic degenerative changes associated with prolonged reproductive inactivity
However, these mechanisms are largely based on clinical experience rather than definitive experimental proof. As far as we know, there are no large-scale studies on this topic. If you know of one, please let us know!
There is some fascinating observational evidence
One paper examined a semi-feral Shetland-type pony herd in which mares typically conceived as yearlings and then foaled every year for life, often into their 30s.
The researchers found:
- remarkably high fertility throughout life
- little apparent decline in reproductive efficiency
- very similar endometrial histology between younger and older mares
This is fascinating because it contrasts with the decline usually seen in domestic broodmares. The authors suggest that continuous reproductive activity under natural conditions may be associated with lifelong reproductive health, although they do not conclude that annual breeding alone causes this outcome. Other factors — such as genetics, environment, nutrition, and natural management — are likely important.
Why a breeding soundness examination is important
Breeding is expensive and there is no way around that fact, but often, investing in a pre-breeding exam can save you money. The last thing you want to do is fork out for a stud contract, shipping and collection, and vet fees to inseminate, only to discover after you have already paid it all that your mare can't conceive.
A reproductive examination may include:
- Ultrasound examination
- Evaluation of the uterus and ovaries
- Assessment of cervical function
- Examination of vulvar and perineal conformation
- Uterine culture or cytology when indicated
- Endometrial biopsy in selected cases
Signs it may be time to retire a broodmare
Here are some of the signs that it might be time to retire your beloved older broodmare and let her live out the rest of her days as the nursery nanny:
- Repeated pregnancy loss
- Chronic uterine issues
- Repeated failure to conceive
- Significant pregnancy or foaling-out complications
- Medical conditions that increase pregnancy risk
- Poor overall health or body condition
For some mares, retirement may occur in their mid-teens. Others continue producing healthy foals well into their twenties.
Keeping accurate breeding records
As mares age, detailed reproductive records become increasingly valuable.
Tracking information such as:
- Heat cycles
- Breeding dates
- Ovulation
- Pregnancy examinations
- Veterinary treatments
- Previous foaling history
- Pregnancy losses
- Reproductive procedures
helps veterinarians identify trends and make better breeding decisions each season.
Managing older broodmares with StallionApp
Managing an older broodmare often requires more careful planning, closer veterinary monitoring, and accurate record keeping than managing a younger mare.
StallionApp allows breeders to maintain a complete reproductive history for every mare, including breeding events, pregnancy checks, foaling records, veterinary procedures, and health information. Having a lifetime breeding record available in one place helps breeders and veterinarians make informed decisions as mares progress through their breeding careers.
Even if it is a mare that you have had for 10 years, having detailed records over those years will highlight when things start to change for her. We all love to think that we are paying attention and will notice things, but in reality, we often miss stuff. Not because we don't care, but because we are tired and busy.
Final thoughts
There is no age at which every broodmare should automatically retire.
While fertility generally declines after about 15 years of age, many mares continue to conceive, carry healthy pregnancies, and raise healthy foals into their twenties.
The best breeding decisions are based on the mare's individual health, reproductive history, and veterinary assessment — not simply her age.
With good management, regular veterinary care, and careful record keeping, many older broodmares continue to make valuable contributions to breeding programs for years beyond what many people might expect.