Can Performance Mares Exercise While Breeding or Pregnant?

By Dr Duncan Houston

Breeding a performance mare is always a balancing act. You want the mare fit, sound, and mentally settled, but you also want the best chance of ovulation, fertilisation, embryo recovery, early pregnancy survival, and eventually a healthy foal.

The mistake is thinking this is a simple yes or no question. Exercise is not automatically bad for fertility. A fit mare is not automatically a poor breeding candidate. But intense work, heat stress, dehydration, travel stress, poor timing around ovulation, and a packed competition schedule can all work against reproduction.

The real question is not, “Can she exercise?” It is, “What type of exercise, in what weather, at what stage of the cycle or pregnancy, and what are we trying to achieve this season?”

Quick Answer

Performance mares can often continue light to moderate exercise during breeding and pregnancy, but heavy work in hot, humid conditions around ovulation may reduce embryo recovery and embryo quality. One study found embryo recovery was lower in exercised mares worked daily for 30 minutes in conditions above 30°C and over 50% humidity, compared with non-exercised controls. Exercise decisions should be based on breeding timing, heat stress, mare age, uterine health, workload, and whether the goal is carrying a pregnancy or using embryo transfer. (PubMed)

Why Performance Mares Are Different

Performance mares are often managed very differently from traditional broodmares. They may be:

• In full work

• Travelling regularly

• Competing

• Stabled away from home

• Exposed to heat and humidity

• Under saddle during the breeding season

• Receiving medications or supplements

• Carrying old injuries

• Older before their first breeding attempt

• Managed through embryo transfer rather than carrying the foal themselves

None of these automatically means the mare cannot get pregnant. But each adds a layer of risk or complexity.

In practice, the mares that cause the most frustration are the ones where the owner is trying to do everything at once: peak performance, repeated travel, heat-season competition, breeding, embryo flushing, and early pregnancy management. The mare is not a machine. Her ovaries, uterus, hormones, immune system, hydration status, and stress response are all part of the same animal.

Does Exercise Reduce Fertility in Mares?

Exercise can reduce fertility in some situations, but the details matter.

The strongest concern is not quiet hacking, turnout, hand walking, or sensible fitness work. The concern is moderate to intense exercise that raises body temperature and stress hormones, especially in hot and humid conditions around follicle development, ovulation, fertilisation, and early embryo development.

A key study on exercised mares found that mares worked daily for 30 minutes in hot and humid conditions ovulated from smaller follicles, took longer from prostaglandin treatment to ovulation, and had lower embryo recovery than non-exercised mares. Embryo recovery was reported as 63% in controls compared with 34% in exercised mares. (PubMed)

A later study on moderate exercise and early embryonic outcomes found exercise increased cortisol concentrations and reduced embryo recovery rates in exercised mares compared with controls, while rest from ovulation to embryo collection did not clearly rescue recovery rates. (PubMed)

The practical takeaway: the highest-risk window is not the whole pregnancy. It is the period around follicle maturation, ovulation, fertilisation, and the first days of embryo development.

Heat and Humidity Are the Big Multipliers

A mare working in cool weather is not the same as a mare working hard in hot, humid conditions.

Heat and humidity make it harder for the mare to lose body heat. Add exercise, transport, competition stress, dehydration, and poor airflow, and her internal temperature and stress response can rise quickly.

This matters because the oocyte, follicle, uterine environment, and early embryo are sensitive biological systems. The studies that raise concern about exercise and fertility often involve heat load, not just movement. In the hot-humid exercise study, mares were worked under average conditions above 30°C and greater than 50% humidity. (Mad Barn USA)

This is where owners need to be practical. A 20-minute walk in the cool of the morning is a very different reproductive risk from canter sets at 1 pm in a humid summer breeding season.

Does Cortisol Affect Mare Fertility?

Cortisol is one of the stress hormones that rises with physical stress, heat stress, pain, transport, illness, and intense exercise. It is not automatically “bad,” because the body needs cortisol. The problem is repeated or significant stress at sensitive reproductive times.

Exercise studies in mares have reported increased cortisol in exercised groups, and researchers have suggested stress physiology may be one pathway by which exercise and heat affect embryo recovery and quality. (ResearchGate)

That said, cortisol is not the only factor. Heat load, ovarian blood flow, follicle wall perfusion, oocyte quality, uterine environment, hydration, and timing around ovulation may all matter. It is too simplistic to say, “Cortisol caused it.” The more accurate version is: stress physiology is part of the fertility picture, especially when combined with heat and hard work.

Is Transport Stress as Bad as Exercise?

Transport can raise stress hormones, but transport is not the same as intense exercise in heat.

Short, calm, well-managed transport for breeding or veterinary reproductive work is usually unavoidable and often acceptable. The larger concerns are long trips, poor ventilation, dehydration, repeated competition travel, heat exposure, social stress, and arriving exhausted or sick.

A single sensible trip to the breeding clinic is very different from a mare competing hard all weekend, travelling overnight, arriving dehydrated, then being bred during a narrow ovulation window. The first is normal reproductive management. The second is asking a lot.

Can a Mare Exercise During Early Pregnancy?

Once a mare is confirmed pregnant, the discussion changes.

Exercise after pregnancy is established is not automatically harmful. A study of mares exercised from day 16 to day 80 of pregnancy reported that exercise during that period did not appear harmful to the developing fetus. (ovid.com)

But this does not mean every pregnant mare should stay in full competition work without adjustment. The type of work, intensity, footing, heat, travel, temperament, previous pregnancy loss, placental concerns, lameness, and veterinary findings all matter.

A mare with a normal early pregnancy, good health, and no reproductive risk factors may tolerate sensible exercise well. A mare with repeated early pregnancy loss, uterine disease, placentitis risk, poor body condition, heat stress, or heavy travel needs a more conservative plan.

The Early Pregnancy Timeline That Matters

Early pregnancy in mares has several key checkpoints.

Merck Veterinary Manual describes one common pregnancy-check schedule as scanning at days 14 to 18 to confirm pregnancy and check for twins, days 25 to 30 to assess embryo development and heartbeat, days 40 to 60 to evaluate fetal development, and a later fall check to confirm the mare remains pregnant. (Merck Veterinary Manual)

The equine embryo is mobile in the uterus from around day 6 to day 16 after ovulation, then becomes fixed around day 16 to 17. This is one reason timing matters so much when planning scans, twin checks, breeding decisions, travel, and workload. (Merck Veterinary Manual)

A practical breeding schedule often looks like this:

This is not about wrapping the mare in bubble wrap. It is about not stacking unnecessary stress during the most sensitive reproductive windows.

Carrying the Foal vs Embryo Transfer

For performance mares, embryo transfer can be a very useful option.

Merck Veterinary Manual notes that embryo transfer is used for performance mares that need to remain nonpregnant to continue training and competing, and that most breed associations now allow registration of foals born by embryo transfer. (Merck Veterinary Manual)

Embryo transfer may make sense when:

• The mare is actively competing

• The mare is too valuable to remove from work

• The mare has a history of pregnancy loss

• The mare has physical issues that make carrying a foal risky

• The owner wants multiple foals from one mare in a season

• The mare is older and embryo production is being prioritised

• The mare’s performance career and breeding goals overlap

However, embryo transfer still requires reproductive management. The donor mare still needs follicle tracking, insemination or breeding, ovulation timing, and embryo collection. Merck notes that daily ultrasound of donor and recipient mares during estrus helps determine ovulation timing and embryo collection day, and that embryo collection is usually performed on day 7 or 8 after ovulation. (Merck Veterinary Manual)

So embryo transfer solves the “can she carry while competing?” issue. It does not remove the need to protect the oocyte, embryo, and reproductive timing.

Severity and Risk Framework

Low Risk: Fit Mare, Light Work, Cool Conditions

This mare is healthy, cycling normally, in good body condition, working lightly or moderately, not overheating, not travelling excessively, and has normal reproductive exams.

What to do: continue sensible exercise, monitor the cycle properly, and avoid hard work around ovulation if breeding success is the main goal.

Medium Risk: Active Training During Breeding Season

This mare is in regular work, may be travelling, and is being bred or flushed for embryo transfer.

What to do: coordinate the training plan with the reproduction vet. Reduce intense work in the days around ovulation, fertilisation, and embryo collection. Keep the mare cool, hydrated, and on a consistent routine.

High Risk: Heavy Work in Heat Around Ovulation

This mare is doing hard sessions in hot or humid weather around breeding, ovulation, or embryo flush timing.

What to do: treat this as a real fertility risk. Shift exercise to cooler times, reduce intensity, use active cooling, prioritise reproductive monitoring, and consider embryo transfer if performance cannot be paused.

Critical Risk: Sick, Overheated, Painful, or Pregnant With Warning Signs

This mare is heat stressed, dehydrated, febrile, colicky, lame, has abnormal discharge, premature udder development, suspected placentitis, or early pregnancy loss concerns.

What to do: stop training and contact your vet. This is no longer a scheduling problem. It is a medical and reproductive risk.

What Else Affects Pregnancy in Performance Mares?

Exercise is only one factor. Focusing only on training can make you miss the real reason a mare is not getting pregnant.

Important rule-outs include:

Mare Age

Older mares often have reduced oocyte quality, more uterine fluid problems, and higher risk of early pregnancy loss. A 17-year-old maiden performance mare is not the same breeding project as a 6-year-old mare with a clean reproductive history.

Uterine Fluid and Endometritis

Post-breeding uterine inflammation and fluid can reduce pregnancy success. Performance mares that are older, have poor uterine clearance, or have cervical issues may need more intensive reproductive management.

Poor Ovulation Timing

Breeding too early, too late, or without ultrasound monitoring can reduce conception. Performance schedules should not dictate breeding timing. The follicle and uterus should.

Semen Quality

Frozen semen, cooled semen, poor motility, delayed transport, and stallion factors can all affect pregnancy rates. Do not blame the mare’s training until the semen side is assessed.

Heat Stress

Hot weather affects more than comfort. It can affect hydration, stress hormones, and possibly oocyte and embryo environment, especially when combined with exercise. (Mad Barn USA)

Poor Body Condition

Thin mares may cycle poorly and may be harder to maintain in pregnancy. Overweight or metabolically abnormal mares may have other risks. Performance mares can look fit but still be nutritionally under-supported for reproduction.

Pain and Lameness

Chronic pain increases stress and can change appetite, movement, sleep, and hormonal balance. A mare trying to breed while managing lameness or back pain needs assessment.

Medications and Competition Rules

Some medications may affect reproduction, pregnancy safety, competition eligibility, or embryo transfer timing. Always tell your reproduction vet what the mare is receiving.

Twins

Mares are not designed to carry twins safely. Early ultrasound is essential. Merck’s pregnancy schedule includes checking for twins at days 14 to 18 and rechecking development at days 25 to 30. (Merck Veterinary Manual)

When Is This an Emergency?

Breeding management itself is not usually an emergency, but some signs in a performance mare should stop training and trigger veterinary help.

Call your vet urgently if a breeding or pregnant mare has:

• Collapse or severe heat stress

• Laboured breathing after exercise

• Persistent high temperature

• Severe dehydration

• Colic signs

• Vaginal bleeding

• Abnormal vaginal discharge

• Fever with discharge

• Premature udder development

• Milk leakage well before foaling

• Sudden severe lameness

• Suspected trauma or fall

• Laminitis signs

• Severe depression or refusal to eat

• Known pregnancy with suspected loss

• Placental or fetal concerns on ultrasound

Merck Animal Health lists pregnancy warning signs such as precocious udder development, premature lactation, vaginal discharge, prolonged gestation, agalactia, dystocia, and placental problems as issues that require veterinary attention during broodmare management. (Merck Animal Health USA)

If the mare is pregnant and unwell, do not treat it as “just a training issue.” The mare and pregnancy both need consideration.

What Should You Do Next?

1. Decide the Priority for the Season

Be honest. Is the priority competition, pregnancy, embryo transfer, or simply preserving future fertility?

Trying to prioritise everything equally usually creates a messy plan.

2. Get a Reproductive Exam Before Breeding

This is especially important for older mares, maiden performance mares, mares with previous pregnancy loss, mares with fluid after breeding, and mares coming out of a heavy competition schedule.

Your vet may assess:

• Uterus

• Ovaries

• Cervix

• Uterine fluid

• Culture or cytology if needed

• Perineal conformation

• Cycle stage

• Follicle development

• Previous breeding history

3. Track Ovulation With Ultrasound

Do not guess. Performance mare breeding needs accurate timing.

Ultrasound helps decide when to breed, when to induce ovulation, when to flush for embryo transfer, and when to check pregnancy.

4. Reduce Intense Work Around Ovulation

If fertility is the priority, avoid hard training in the days leading up to and immediately after ovulation, especially in hot or humid weather.

Light work, walking, turnout, and gentle movement are usually more sensible than full gallops, hard canter sets, or heavy schooling sessions in heat.

5. Manage Heat Aggressively

Use:

• Early morning or evening work

• Shade

• Fans

• Active cooling

• Electrolytes when appropriate

• Good water access

• Reduced intensity in humidity

• Longer cool-downs

• Transport ventilation

6. Avoid Over-Scheduling

Do not breed, compete, transport, medicate, scan, and flush without a coordinated plan. Reproduction works best when the whole team is aligned: owner, trainer, rider, vet, stud, and embryo transfer centre.

7. Confirm Pregnancy Properly

Use the standard ultrasound checkpoints. Merck describes days 14 to 18 for pregnancy and twin check, days 25 to 30 for development and heartbeat, days 40 to 60 for fetal development, and a later confirmation check. (Merck Veterinary Manual)

8. Consider Embryo Transfer Early

If the mare needs to stay in serious work, discuss embryo transfer before the season becomes chaotic. Merck notes that embryo transfer is used for performance mares that must remain nonpregnant to train and compete. (Merck Veterinary Manual)

9. Do Not Ignore Pain

A sore mare is a stressed mare. Manage lameness, saddle fit, back pain, dental pain, and systemic illness before expecting reproductive performance.

10. Reassess If She Does Not Conceive

If the mare fails to conceive, do not simply repeat the same plan. Review uterine health, semen quality, ovulation timing, age, heat stress, exercise intensity, transport, and embryo transfer options.

Common Mistakes Owners Make

Blaming Exercise for Everything

Exercise can matter, but it is not the only cause of poor fertility. Age, uterine disease, semen timing, fluid, inflammation, twins, and embryo quality may matter more.

Keeping Full Training Through the Ovulation Window

If breeding success is the goal, this is the period to be conservative, especially in heat.

Forgetting Weather

The same workload can be low risk in cool conditions and much higher risk in hot, humid conditions.

Scanning Too Late for Twins

Twin checks need to be early. Waiting too long makes management harder and may risk losing the season.

Trying Embryo Transfer Without Adjusting the Training Plan

Embryo transfer still relies on oocyte quality, ovulation timing, fertilisation, and embryo recovery. The donor mare still matters.

Ignoring the Mare’s Age

Many performance mares are bred later in life. A reproductive plan for an older maiden mare needs to be more proactive.

Treating Transport as Harmless Every Time

One sensible trip is usually fine. Repeated long travel, heat, dehydration, competition stress, and poor recovery are different.

Can Performance Mares Stay Fit During Pregnancy?

Often, yes, but the exercise plan should change as pregnancy progresses.

For a normal, healthy pregnancy:

• Light to moderate exercise can often continue

• Turnout is usually beneficial

• Avoid overheating

• Avoid extreme fatigue

• Avoid risky footing

• Avoid high-impact work if the mare is uncomfortable

• Reduce intensity as pregnancy advances

• Stop work if the mare shows pain, illness, abnormal discharge, or pregnancy concerns

The goal is not to make the mare unfit. The goal is to keep her healthy without creating unnecessary risk.

A useful rule: fitness work should support the pregnancy, not compete with it.

Prevention: A Better Breeding Plan for Performance Mares

A strong plan should include:

• Pre-breeding reproductive exam

• Body condition assessment

• Review of medications and supplements

• Soundness and pain check

• Cycle tracking

• Ovulation timing

• Heat and humidity management

• Training adjustment around ovulation

• Pregnancy scan at days 14 to 18

• Twin check

• Heartbeat check at days 25 to 30

• Follow-up check at days 40 to 60

• Embryo transfer discussion if she must stay in work

• Clear communication between trainer and vet

• Plan for poor embryo recovery or failed conception

• Cooling and hydration strategy during summer breeding

The best fertility plan is not just “breed her and hope.” It is a coordinated management plan that respects both the athlete and the broodmare.

FAQ

Can I ride my mare while trying to breed her?

Yes, many mares can continue light to moderate work while being bred. The higher-risk situation is intense exercise around ovulation, especially in hot and humid weather.

Should I stop all exercise after insemination?

Not always. Complete rest is not automatically required, but if fertility or embryo recovery is the priority, reduce intense work during the ovulation and early embryo window. Keep the mare cool, hydrated, and settled.

Can exercise cause early pregnancy loss in mares?

Exercise is not the only cause of early pregnancy loss, but heavy work, heat stress, systemic illness, pain, poor uterine health, and stress may contribute. Early pregnancy loss is multifactorial, so your vet should assess the mare, semen, timing, uterus, and management plan.

Is embryo transfer better for performance mares?

Embryo transfer can be very useful if the mare needs to keep competing or should not carry a foal. It allows a recipient mare to carry the pregnancy, but the donor mare still needs careful reproductive management and embryo collection timing. (Merck Veterinary Manual)

When should a performance mare have her first pregnancy scan?

A common schedule is to scan at days 14 to 18 after ovulation to confirm pregnancy and check for twins, then recheck around days 25 to 30 for development and heartbeat. (Merck Veterinary Manual)

Final Thoughts

Performance mares can be bred successfully, but they need a smarter plan than “keep training and see what happens.”

Exercise itself is not the villain. The real risks are timing, heat, intensity, stress, poor reproductive monitoring, mare age, uterine disease, and trying to chase competition and pregnancy without adjusting anything.

If pregnancy is the priority, protect the ovulation and early embryo window. If competition is the priority, discuss embryo transfer early. If both matter, your mare needs a coordinated plan between the trainer and reproduction vet.

A performance mare can be an athlete and a breeding mare. She just should not be expected to do both at full pressure without a plan.

If you are breeding a performance mare and are unsure how to balance training, heat, travel, embryo transfer, or early pregnancy checks, ASK A VET™ can help you work through the risks and decide when veterinary reproductive support is needed.