Mare Reproductive
Calendar & Planner
Enter your mare's service date or last cycle to get a predicted foaling date, full pregnancy milestone calendar, recommended pregnancy checks, and a complete breeding season management plan.
Tell us about your mare
We'll use this to personalise your reproductive calendar and management recommendations.
Breeding information
Enter your mare's service date or last cycle date to calculate her foaling date.
If you have multiple service dates, use the most recent confirmed ovulation date.
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We'll email your personalised mare reproductive calendar with all key dates and management reminders.
Your Mare Reproductive Calendar
Your personalised calendar has been emailed. Save the key dates below.
Mare Reproduction — A Complete Guide for Horse Owners
Understanding your mare's reproductive cycle is the foundation of successful breeding management. Whether you are breeding for the first time or managing an established breeding programme, knowing the key milestones and management requirements at each stage of pregnancy will help you achieve the best outcomes for your mare and foal.
The Mare's Reproductive Cycle
Mares are seasonally polyoestrous — they cycle during the longer days of spring and summer and enter a period of reproductive rest (anoestrus) during winter. In Australia, the natural breeding season runs from approximately September to February, with peak fertility in October, November, and December. The mare's oestrous cycle averages 21 days, with oestrus (heat) lasting 5–7 days and ovulation occurring approximately 24–48 hours before the end of oestrus.
Key Pregnancy Milestones
The following milestones are the most important management points during a mare's 340-day pregnancy:
Day 14–16: First pregnancy check by rectal ultrasound. This is the earliest reliable detection of pregnancy and is essential for identifying twin pregnancies, which must be reduced to a singleton for the best outcome.
Day 28–30: Second pregnancy check. Confirms heartbeat and viability. Strongly recommended.
Day 45: Third pregnancy check. Confirms embryo viability and Endometrial cups forming. Foetal sexing is possible from this point on. Optimum time for foetal sexing.
Day 60 (Optional): Fourth pregnancy check. Confirms ongoing pregnancy and foetal development. Recommended for maiden mares and high-value pregnancies. Placenta takes over progesterone production around day 60–90. Discuss discontinuing supplementation with your vet if your mare is being supplemented.
Day 270: Increase energy, calcium and protein intake to support foetal growth. The foal gains approximately 60% of its birth weight in the last trimester.
Day 300: Prepare foaling area. Assemble foaling kit. Begin monitoring for signs of impending foaling (waxing, milk let-down, vulval relaxation).
Day 310: Vaccination booster recommended (tetanus and strangles). This primes the mare's colostrum with antibodies for the foal.
The Foal Heat
Mares typically return to oestrus 7–12 days after foaling — this is known as the foal heat. Many breeders choose to breed on the foal heat to maintain a consistent foaling date from year to year. However, foal heat breeding has lower conception rates than breeding on the subsequent cycle (approximately 30 days post-foaling). Your vet can assess uterine involution by ultrasound to determine whether foal heat breeding is appropriate for your mare.
Frequently Asked Questions About Mare Reproduction
Answers to the most common questions horse owners ask about mare breeding and pregnancy.
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