Mare Heat Cycle Calculator
Predict your horse's next estrus and optimal breeding window.
Estimated Breeding Schedule
Understanding the Mare Reproductive Cycle
Successfully breeding horses requires a deep understanding of the mare's reproductive physiology. Mares are seasonally polyestrous, meaning they go through multiple heat cycles during the spring and summer months when daylight is longest. This Mare Heat Cycle Calculator helps owners and breeders predict when their mare will be receptive to a stallion and, more importantly, when she is likely to ovulate.
The Phases of the Equine Estrous Cycle
A typical mare's cycle lasts approximately 21 days, though it can range from 18 to 24 days. The cycle is divided into two primary phases:
- Estrus (Heat): This is the period when the mare is receptive to the stallion. It typically lasts 5 to 7 days. During this time, the mare produces estrogen as follicles develop on her ovaries.
- Diestrus: This is the period between heat cycles when the mare is not receptive. It usually lasts 14 to 16 days. If the mare is not pregnant, her body releases prostaglandins to reset the cycle.
Predicting Ovulation for Breeding Success
The most critical moment for a breeder is ovulation. In most mares, ovulation occurs 24 to 48 hours before the end of the estrus period. Because equine sperm survives for about 48 hours and the egg is only viable for 6-12 hours after release, timing is everything. Our calculator uses the "Ovulation Lead" input to help you pinpoint that 48-hour window before the heat cycle is expected to conclude.
Realistic Calculation Example
Let's say your mare, "Bella," started her last heat on May 1st. You know from previous seasons that her cycle is exactly 21 days and she usually stays in heat for 6 days.
- Last Heat Start: May 1
- Calculated Next Heat: May 1 + 21 days = May 22
- Heat Duration: May 22 to May 27 (6 days)
- Estimated Ovulation: May 25 – May 26 (approx. 2 days before the end)
Factors That Affect the Cycle
While this calculator provides a mathematical estimate, several factors can alter the actual dates:
- Light Exposure: Increased daylight triggers the onset of the breeding season.
- Nutrition: Mares in good body condition tend to cycle more regularly.
- Age: Older mares may have longer or more irregular cycles.
- Weather: Extreme temperature changes can occasionally "stall" a cycle during the early spring.
Frequently Asked Questions
How long is a horse pregnant?
The average gestation period for a mare is approximately 340 days, though it can vary between 320 and 370 days.
What are the signs of a mare in heat?
Common signs include frequent urination, "winking" (opening and closing the vulva), lifting the tail, and showing interest in or receptivity toward stallions.
When should I call the vet?
If you are using artificial insemination (AI) or cooled/frozen semen, veterinary monitoring via ultrasound is essential to confirm the size of the follicle and the exact timing of ovulation.