December 6, 2023

We wish you a MARE-y Christmas

As the festive season prances in - – it’s a sign that a very MARE-y Christmas is upon us! Whether they’re daintily stepping through the snow or spiritedly kicking up a frosty cloud in their stalls, mares add an undeniable sparkle to the holiday season. From their heartwarming nuzzles to their sometimes frosty moods, we’re diving into what makes these creatures tick—or should we say, trot—during their heat cycles.

Get ready for a sleigh-full of insights in our 'We Wish You a MARE-y Christmas' post. And remember, while the weather outside may be frightful, the company of mares is mostly delightful! 😉

Understanding the Mare’s Estrous Cycle

Mares usually mature between 12 and 15 months of age, kicking off their reproductive capability. The Mare's estrous cycle, not to be confused with estrus itself, the "in heat" phase, is seasonally polyestrous, meaning they ovulate during specific times of the year. The cycle stabilizes into a predictable pattern typically from mid-April through mid-September, aligning with the optimal breeding season for horses. A mare’s cycle lasts about 21-22 days and comprises two distinct phases:

  1. Estrus Phase: This is when the mare is "in heat," receptive to the stallion and biologically primed for breeding. The duration of estrus varies from one mare to another, generally spanning six days but ranging from four to ten days.
  2. Diestrus Phase: During this time, the mare is "out of heat" and not receptive to breeding. This phase usually extends over 15 days, but it can vary slightly.

Come September, as the photoperiod wanes, mares enter anestrus, a period where they cease to cycle normally.

Ovulation, the release of the egg ripe for fertilization, typically occurs between 24 and 48 hours before estrus concludes. For breeders aiming for conception, timing is paramount; mating the mare within 12 hours post-ovulation is ideal.

The first estrus of the year can be an unpredictable affair, often drawn out, with mares in heat for extended periods of 20-30 days or more. However, as spring deepens into summer, regularity becomes the norm, with most mares showing clear signs of sexual receptivity.

It's essential to note that early spring heats may not always lead to ovulation. This is why breeders will often rely on rectal palpation to confirm follicular development before proceeding with breeding plans.

The Entire Cycle is Controlled by Hormones

The estrous cycle is an intricate hormonal dance orchestrated by the mare's endocrine system. The pituitary gland, nestled at the brain's base, responds to the incremental daylight by upping its production of follicle-stimulating hormone (FSH), which then journeys to the ovaries, spurring the growth of a follicle that houses an ovum. As the follicle matures, it secretes estrogens that circulate in the bloodstream.

When estrogen levels hit their peak, the pituitary gland releases a burst of luteinizing hormone (LH), leading to the follicle's rupture and, subsequently, ovulation.

What follows is nothing short of reproductive alchemy. The empty follicle transforms into a corpus hemorrhagicum, which then evolves into the corpus luteum. This new structure begins to secrete progesterone, a hormone that, through its feedback loop, suppresses LH release and curtails estrus behaviors. Progesterone's key role is to prepare and maintain the uterus for a potential pregnancy, fostering an environment suitable for fetal development.

This seasonal tale of hormonal interplay is not just a matter of scientific fascination but a practical guidepost for breeders and horse owners alike. By understanding the ebb and flow of the mare's natural cycles, we're better equipped to manage breeding programs, interpret behaviors, and ensure the health and well-being of these remarkable animals throughout the year.

Spotting the Signs of Heat

When mares go into heat, they may exhibit a variety of behavioral and physical symptoms due to the hormonal changes they experience. Here's a detailed look into these signs:

Physical Symptoms:

  1. Tail Raising: Mares often raise their tails more frequently and hold them to one side, a behavior known as "flagging."
  2. Vulval Changes: You may notice the vulva swelling and the mare 'winking' or flickering her clitoris.
  3. Urine Spurts: Frequent urination or squirting urine is common as a signaling behavior to potential mates.
  4. Discharge: A clear or slightly cloudy mucus discharge can occur, which is different from the typical signs of infection.
  5. Ovarian Discomfort: Some mares show signs of discomfort due to ovarian activity, which might include flinching when touched near the flank or showing resistance to saddling.

Behavioral Symptoms:

  1. Increased Interest in Stallions: Mares in heat will often show a heightened interest in stallions and can be overly attentive to other horses.
  2. Restlessness: Mares may appear more restless than usual, pacing in their stalls or paddocks.
  3. Changes in Eating and Sleeping Patterns: There may be a noticeable decrease in appetite and changes in sleeping habits.
  4. Mood Swings: Mares can exhibit mood swings, appearing more irritable or anxious during their heat cycle.
  5. Vocalization: Increased whinnying or neighing, especially in response to other horses, is a common sign.
  6. Kicking: Mares might kick at their stall walls or towards other horses as a sign of irritability or discomfort.
  7. Squatting Posture: Adopting a straddling or squatting posture as if to urinate, often without actually doing so, is a typical sign of estrus.

Managing Behaviors:

Treatment and management of mares, particularly those showing signs of discomfort or behavioral changes due to their estrous cycle, can be addressed through several methods. Each option has its specific applications and potential outcomes:

Progesterone Therapy:

  1. Oral Altrenogest (Regu-Mate): A synthetic progestin that keeps mares out of estrus by maintaining them in a state of diestrus. It requires daily administration.
  2. Injectable Altrenogest: Can suppress estrus in mares, but some may develop muscle soreness from injections.

Non-Hormonal Treatments:

  1. Marble Implantation: Placing a marble in the mare's uterus at ovulation can prevent her from coming into heat for up to 90 days. It's not effective for all mares, but it's a non-drug approach and doesn't require daily management.
  2. Oxytocin Injections: Administered twice a day on specific days after ovulation, it has been shown to keep mares out of heat for extended periods.

Surgical Options:

  1. Ovariectomy: The surgical removal of ovaries can be a solution to problematic estrous behaviors, but it's irreversible and eliminates the mare's fertility.

Hormone Treatments:

  1. GnRH Vaccine: A vaccination that induces ovarian quiescence, reducing estrous behaviors by affecting the release of Gonadotropin-Releasing Hormone.
  2. Depo-Provera (medroxyprogesterone acetate): Used by some, but research suggests it doesn't reliably suspend cycling. This is no longer legal for competitions.

Alternative Therapies:

  1. Acupuncture: Used to regulate the hormonal sphere and ovarian activity.
  2. Phytotherapy: Herbal treatments such as chamomile, lemon balm, or hops can have antispasmodic and anti-inflammatory effects.

Environmental and Behavioral Management:

  1. Environment: Ensure the mare's environment is comfortable, and consider changes that might reduce stress, such as offering more turnout time.
  2. Handling: Adjust handling techniques to accommodate the mare's increased sensitivity, approaching and touching her more gently, especially around the flank and hindquarters.
  3. Training: It may be wise to alter training schedules to account for behavioral changes, choosing less intense work or focusing on ground exercises during peak heat days.
  4. Journaling: Keeping a detailed behavior journal can help determine if undesirable behaviors are linked to the estrous cycle.

Each of these methods requires consideration of the individual mare's needs, behaviors, and health status, as well as consultation with a veterinarian to determine the most appropriate approach. The goal of these treatments is to ensure the well-being of the mare while minimizing any negative impact on her behavior and performance.

Balancing Mare Moods: The Role of Nutrition and Supplements

When it comes to mares, their mood swings and unpredictable behaviors can often be attributed to hormonal imbalances. These can impact not just their demeanor but their overall health and performance. Enter the world of horse supplements, which can provide the essential nutrients required to support hormonal balance and manage mood-related issues.

Estrogen and Progesterone in Mares:

  • Estrogen levels fluctuate throughout the mare's estrous cycle, commonly rising in spring with increased daylight. Higher estrogen levels are associated with "heat" behavior.
  • Progesterone prepares the uterus for pregnancy and inhibits estrus behavior. Fluctuating levels can influence mood and receptiveness to stallions.

Nutritional Support for Hormonal Health:

  • A balanced diet, rich in specific nutrients like magnesium and Vitamin E, is essential for hormonal function. Deficiencies can lead to imbalances, while a nutritious diet supports hormonal health.

Horse Supplements:

  • Supplements often contain herbs like chasteberry, which supports pituitary health, and raspberry leaf, known for reproductive benefits.
  • Magnesium supplements are known for their calming effects and can help regulate stress hormones, contributing to a more even-tempered mare.
  • Other ingredients, such as valerian, chamomile, and dandelion, support the nervous system and may help stabilize temperament.

Feeds to Be Cautious Of:

  • Some feeds, like soy and alfalfa, contain phytoestrogens, which can disrupt hormonal balance. Monitoring and potentially reducing intake of these feeds may improve behavior.

When to Seek Veterinary Advice:

  • If behavioral changes are persistent or there is physical discomfort, it is crucial to consult a veterinarian for a thorough assessment and appropriate treatment.

Considering Supplements:

Ultimately, understanding the complex hormonal system of mares and providing the right nutritional and supplemental support can lead to a more harmonious relationship with these sensitive creatures. While empirical evidence supports the use of supplements, scientific research is limited. Consult with an equine nutritionist or veterinarian before adding new supplements to your mare's regimen to ensure they are necessary and appropriate for your horse's specific needs.


In summary, understanding and caring for mares demand an awareness of their reproductive cycles and the associated behavioral changes. Whether managing a mare for riding, breeding, or companionship, recognizing these nuances ensures a harmonious relationship between the mare and her caretaker.