You know a horse is in heat, also called estrus, by watching for specific body language and changes in behavior. These signs of mare in season help owners know when a mare is ready to breed.
Deciphering the Equine Estrous Cycle
To spot when a mare is ready, it helps to know about her natural rhythm. The estrous cycle in mares dictates when she is fertile. This cycle repeats roughly every 21 days. It has two main parts. The mare is fertile during estrus (heat). She is not fertile during diestrus (the resting phase).
The Phases of Estrus
Estrus is the time when the mare accepts the stallion. It usually lasts about five to seven days. This is when mare ovulation signs become important. After heat, the mare enters the luteal phase, or diestrus. This period lasts about 14 to 16 days. She will usually reject a stallion during this time.
| Phase | Approximate Duration | Mare Behavior | Key Hormones |
|---|---|---|---|
| Estrus (Heat) | 5–7 days | Receptive to breeding | Estrogen high |
| Diestrus (Rest) | 14–16 days | Rejects stallion | Progesterone high |
Identifying Behavioral Signs of Mare in Heat
Observing the mare’s actions is the best first step. Behavioral signs of mare in heat are often the most obvious clues. A mare in heat acts very differently from one that is not.
Vocalizations and Restlessness
Mares in heat can become noisy. They might vocalize more often. You might hear them squeal or nicker. They can also seem restless. They may pace more in their stall or field. This change in mood shows something is happening inside.
Seeking Out Males
A mare in season often looks for stallions or geldings. She might try to get closer to male horses. She might stand near the fence line. This shows her strong drive to mate. These are strong equine heat signs.
Tail Raising and Winking
This is a classic sign. A mare in heat often lifts her tail when a stallion approaches or when you tease her. She may also show “winking” or “flagging.” This means she rapidly opens and closes her vulva lips. This action exposes the clitoris. It is a clear signal of mare readiness to breed.
Standing Still for Attention
When a mare is receptive, she will often stand quietly for a stallion. She will hold still for him to sniff or nuzzle her. A mare not in heat will usually move away or kick at the approaching male.
Physical Signs of Mare in Heat
Besides behavior, there are physical changes to look for. These signs mare is receptive are often seen when you clean or check her hindquarters.
Swollen Vulva
The vulva of a mare in heat often appears slightly swollen or puffy. It may look pinker than usual. This is due to increased blood flow to the area. This physical change supports the behavioral clues.
Increased Urine and Scent Output
Mares in heat pass urine more often. They often squat slightly when urinating. This releases scent signals, or pheromones, into the urine. These scents attract stallions.
Discharge
While not always present, some mares show a clear, stringy discharge when in heat. This fluid comes from the reproductive tract. It is a sign that the reproductive system is active.
How to Confirm Heat: Teasing the Mare
Veterinarians and experienced horsemen often use a specific method to confirm heat. This is called teasing a mare for heat. This method involves safely introducing the mare to a stallion or a teasing cross.
The Teasing Process
Always prioritize safety. Teasing should only happen with experienced handlers present. A safe, sturdy chute or breeding stall is best. The teaser animal (often a gelding or a stallion) is brought close to the mare.
- Observe Initial Reaction: Watch how the mare reacts immediately. Does she turn toward the teaser? Does she pin her ears back?
- Observe Standing: If she is receptive, she will stop moving. She will lower her head and lift her tail. This means signs mare is receptive to stallion.
- Checking for Winking: A handler can safely stand near the mare’s flank (side). Gently rub her back or lift her tail slightly. Watch for vulvar winking.
If the mare shows no interest, moves away, or shows aggression (kicking, biting), she is likely not in heat. She is probably in diestrus.
Using Gels for Teasing
Some handlers use specialized teasing gels on geldings or collection dummy mounts. These gels mimic the scent of a mare in peak heat. This can help gauge a stallion’s interest without the risks of direct exposure.
Veterinary Aids in Detecting Estrus
While observation is key, modern techniques offer more precision. These methods help pinpoint the exact moment of mare ovulation signs.
Ultrasound Examination
The gold standard for timing breeding is the rectal ultrasound. A veterinarian inserts a probe into the rectum. They look at the ovaries.
- Follicle Growth: As heat approaches, a fluid-filled sac called a follicle grows on the ovary. This sac holds the egg.
- Follicle Size: When the follicle reaches a certain size (usually 35–50 mm), the mare is close to ovulation.
- Uterine Appearance: The lining of the uterus changes color and texture on the ultrasound screen when the mare is in heat. It looks “honeycombed” or wet.
Hormone Testing
Blood tests can measure hormone levels. Progesterone stays low during estrus. Estrogen levels rise just before ovulation. Testing hormone levels confirms the stage of the estrous cycle in mares. This is especially helpful for mares with irregular cycles.
Manual Examination
A veterinarian can perform a vaginal examination. They check the cervix and vaginal walls. A mare in full heat will have a soft, moist cervix. The vaginal lining will look bright red and puffy.
Recognizing When Heat Ends
Knowing when the heat period stops is as important as knowing when it starts. This marks the transition back to the non-fertile phase.
Signs Mare is Receptive Stops
The most immediate sign that heat is ending is a sudden change in reaction to the stallion.
- She stops standing still.
- She turns her hindquarters away quickly.
- She may strike out or swish her tail forcefully when the teaser approaches.
- The vulva swelling will start to decrease.
Post-Estrus Changes
In the days following the end of heat, the mare returns to normal behavior. She ignores teasing attempts. Her appetite and mood stabilize. The hormonal shift toward progesterone production causes these changes.
Factors Affecting Heat Detection
Several things can make spotting equine heat signs difficult. Weather, age, and reproductive history all play a part.
Seasonal Anestrus (Winter Block)
Horses are seasonal breeders. They cycle best when days are long (spring and summer). In winter, many mares enter a transitional period or anestrus. They do not cycle regularly. Heat signs during this time can be very subtle or absent.
“Silent Heats”
Sometimes, a mare is ovulating but shows very few outward signs. These are called silent heats. Experienced handlers look for subtle changes like very brief tail raising or minimal vulvar swelling. Ultrasounds are necessary to catch these mares.
Age and Health
Older mares sometimes have shorter heat periods. Mares with certain reproductive issues, like cysts on the ovaries, might show prolonged or erratic heat behavior.
Comparison Table: In Heat vs. Not In Heat
This table summarizes the key differences you should look for when checking signs mare is receptive.
| Feature | Mare In Heat (Estrus) | Mare Not In Heat (Diestrus) |
|---|---|---|
| Tail Position | Lifts tail high when stimulated | Sits tail down; may swish it away |
| Vulva Appearance | Swollen, pinker, frequent winking | Normal size, less color change |
| Reaction to Teaser | Stands still, solicits attention | Moves away, pins ears, kicks |
| Urine Output | Squats, often deposits small amounts | Normal urination schedule |
| Vocalization | May squeal or nicker | Quiet, focused on normal activity |
| Ultrasound Finding | Large, growing follicle; wet uterus | Corpus Luteum present; dry uterus |
Practical Tips for Consistent Heat Detection
For successful breeding management, you need a routine. Consistent observation leads to accurate breeding decisions.
Establish a Routine Schedule
Check your mares at the same time every day. Early morning and late afternoon are good times. This consistency helps you notice small changes quickly. Keep detailed records of when you see equine heat signs.
Use a Teaser Regularly
Even if you don’t plan to breed immediately, teasing every two to three days during peak season keeps you aware of the cycle status. This prevents missing a short heat window.
Working with Your Veterinarian
Partner with your vet for breeding soundness exams. They can teach you how to spot subtle mare signs of estrus. They can also use ultrasound effectively to time insemination precisely.
Fathoming the Role of Estrogen
Estrogen is the primary hormone driving the heat cycle. High levels of estrogen cause the mare to become receptive. This hormone prepares the reproductive tract for potential pregnancy. It causes the physical swelling and the behavioral changes. When the egg is released (ovulation), estrogen levels drop sharply. Progesterone then takes over, signaling the end of heat. This sharp shift explains why signs mare is receptive disappear so suddenly.
Frequently Asked Questions (FAQ)
How long does a mare usually stay in heat?
A mare typically stays in heat for about five to seven days during the breeding season. This can vary based on the individual mare and the time of year.
Can a mare show signs of heat when she is already pregnant?
Yes, sometimes a pregnant mare can show very mild signs of heat, especially early in pregnancy or if the pregnancy is failing. This is sometimes called “false heat.” Always confirm pregnancy via ultrasound or palpation before attempting to breed a mare.
What should I do if my mare shows no signs of heat in the spring?
If a mare does not cycle when days get longer, she may be in transitional anestrus. You can try extending daylight artificially using bright lights in her stall for 14–16 hours daily. This often encourages the estrous cycle in mares to restart. Consult your veterinarian if cycling does not resume.
How can I safely tease a mare for heat?
Safety is paramount. Teasing should be done in a controlled environment, like a breeding chute, with experienced handlers. Never let an unhandled stallion approach a mare freely in an open field. Use a trained teaser stallion or a safe dummy object if necessary.
Is tail flagging the only sign I need to look for?
No. While tail flagging (lifting and winking) is a very strong indicator that the mare is receptive to stallion, it should always be combined with other observations, such as standing still, reduced movement away from the teaser, and ideally, physical signs like a swollen vulva.