This No. 1 Horse Gestation Calculator is a useful tool to estimate the approximate foaling date for a pregnant mare based on her breeding dates.

A mare’s gestation period from conception to foaling averages 340 days. However, normal gestation in horses ranges from 320-370 days depending on the breed and individual variation.

The average full gestation period for horses is:

• 340 days – From conception to birth, the average is 340 days, based primarily on light horse breeds.
• 11 months – Gestation averages almost 11 months in length. Most mares go over 320 days but under 370 days.
• 48-49 weeks – The full gestation period averages between 48-49 weeks from breeding to foaling.

Horse Gestation Calculator

To use the Equine gestation calculator:

• Enter the breeding dates – Input the first and last dates the mare was bred/inseminated.
• View estimated due date – The calculator will add 340 days to the midpoint between the breeding dates to estimate when foaling will occur.
• The calculator provides a general foaling date estimate. But the actual gestation length and due date may vary.
• Adjust with vet exams – Ultrasounds from 16-120 days into gestation can provide more accurate dates for conception and fetal development.
• Sequential ultrasounds pinpoint the actual due date based on the growth measurements of the fetus.
• Physical signs like udder development and pelvic ligament relaxation also indicate when birth is approaching.

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Horse Gestation Period Timeline

0 Days – The egg is fertilized by a sperm and conception occurs

0-16 Days – The fertilized egg divides and migrates to the uterus for implantation

16-40 Days – Implantation and early placental development; pregnancy can first be detected via ultrasound

40-70 Days – Rapid growth of the embryo; major organ formation

70-90 Days – Development of facial features, limbs, skeleton, muscles

90-120 Days – Fetal movement begins; sex can be determined via ultrasound; organs mature

120-210 Days – Continued growth and musculoskeletal development; mare’s belly enlarges

210-280 Days – Hair coat and hoof growth; mare’s udder begins forming

280-320 Days – Fetus gains fat, muscle, and strength in preparation for birth

320-370 Days – Final rapid fetal growth spurt; waxing udder and pelvic relaxation as foaling nears

320-370 Days – Foaling occurs in 3 stages: cervix relaxation, rupture of the chorioallantois, and active labor/delivery

Postpartum – Expulsion of the placenta completes gestation; mare can come into heat again within 10 days

The key events are fertilization at 0 days, major organ formation from 40-120 days, then continual growth to full term and foaling in months 11-12. Veterinary monitoring tracks the fetal development progress.

340 Day Gestation Table

Gestation Day	Developments
0	Conception – Egg is fertilized by sperm
16-40	Implantation – Egg implants in uterus; pregnancy can be confirmed by ultrasound
40-70	Embryo development – Major organs start forming
70-90	Fetus development – Facial features, limbs, skeleton, muscles develop
90-120	Fetal movement – Sex can be determined on ultrasound; organs mature
120-210	Mid-gestation – Continued fetal growth and musculoskeletal development
210-280	Late gestation – Hair, hooves, and udder start developing
280-320	Preparing for birth – Fetus gains muscle, fat, and strength
320-340	Prelabor – Udder waxing, pelvic ligament relaxation as foaling nears
330-340	Foaling preparations – Mare behavior changes; ideal time for vet check
340	Average Foaling Day – Labor occurs in 3 stages
341+	Postpartum – Placenta expulsion completes gestation; mare can breed again

Key stages include implantation by 40 days post-conception, rapid fetal development from 40-210 days, final preparations for birth from 280-340 days, foaling around 340 days, and postpartum recovery. But veterinary monitoring is needed to track each mare’s actual gestation timeline. This 340 day table provides general guidlines.

What is Gestation in Mares?

Gestation is the period of time from conception to birth. For horses, normal gestation lasts 320-370 days, or approximately 11 months.

On average, light horse breeds like Thoroughbreds and Arabians gestate for 340 days.

Draft horses, such as Clydesdales and Shires, tend to have slightly longer gestation periods around 350 days.

• Fertilization – The gestation clock starts ticking when the mare ovulates and the egg is fertilized by a stallion’s sperm.
• Early fetal development – In the first few weeks after fertilization, the fertilized egg divides and implants in the uterus. Major organ development occurs.
• Fetal growth – In the mid-gestation period, the fetus continues growing rapidly. Hooves, bones, organs, and muscles develop.
• Late gestation – In the final 3 months, the fetus gains muscle and fat. The mare’s belly enlarges and her udder begins producing milk.
• Foaling – Labor occurs in 3 stages – uterus contractions, water breaking, and active labor/birth. Once the placenta passes, gestation is complete.

Estimating a Mare’s Foaling Date

Since the average gestation length is 340 days, an easy starting point is to add 340 days to the breeding date. However, several factors can alter the exact foaling timeline:

• Breed – Pony and draft breeds tend to have slightly longer gestation. Thoroughbreds and Arabians have average length.
• Individual variation – Each mare is different. Her age, reproductive history, and other traits influence gestation length.
• Breeding dates – Accurate breeding dates are critical. Even a few days variance in breeding dates translates to days variance in foaling dates.
• Time of year – Mares bred in late winter/spring tend to carry a bit longer than mares bred in late summer/fall.

To increase accuracy, veterinarians suggest these steps:

1. Identify possible breeding dates – Work with the stallion owner to determine first and last possible dates.
2. Initial foaling estimate – Start with 340 days from the midpoint between first/last breeding dates.
3. Ultrasound check – Around day 16 post-ovulation, an ultrasound can confirm pregnancy and the due date.
4. Monitor fetal development – Sequential ultrasounds from day 45-120 can pinpoint the true due date.
5. 11-month checkup – A late term vet check at 330 days can reveal the foal’s position and alert owners to any issues.

Mare Care During Gestation

Proper mare care is vital for her health and that of the developing foal:

• Nutrition – Balanced diet with adequate calories, vitamins and minerals. Mares need 20-25% more nutrition in the last 3 months.
• Exercise – Regular light exercise prevents excessive weight gain and improves muscle tone for labor and lactation. No intense exercise in late gestation.
• Vaccines – Flu and rhino vaccines in months 5, 7, and 9 boost antibodies to protect the foal. Avoid live vaccines.
• Parasite control – Continue regular deworming. Ivermectin is safe during pregnancy.
• Environment – Comfortable shelter, clean paddocks, and low stress conditions help the mare stay healthy.
• Observations – Monitor for illness, discomfort, vaginal discharge, early lactation, or abnormalities. Alert the vet to any concerns.

With the proper care, most mares can continue regular work and activities throughout gestation. But extra attention to her changing needs prepares her for the critical days ahead.

What is foaling?

Foaling refers to the process of a pregnant mare giving birth to her offspring, also called the foal. It encompasses the final stage of gestation as the mare goes into labor, the foal is delivered, and the afterbirth is passed.

The three stages of foaling are:

1. Positioning of the foal and cervix relaxation as hormones shift
2. Rupture of the chorioallantois (water breaking) and active labor contractions
3. Delivery of the foal followed by expulsion of the placenta

Signs that foaling is imminent include waxing of the teats, swelling of the vulva, relaxation of the tail head, and streaming of milk. Owners should prepare a clean foaling area with supplies to care for the mare and newborn foal.

How to calculate foaling date with horse pregnancy length?

To calculate a mare’s foaling date based on the 340 day average horse pregnancy length:

1. Identify breeding dates – Work with the stallion owner to determine possible insemination dates.
2. Midpoint of dates – Calculate the midpoint between the first and last breeding dates.
3. Add 340 days – Count forward 340 days from the midpoint date identified in step 2.
4. Adjust – Fine-tune the due date using ultrasound exams to date conception based on fetal development and growth.
5. Monitor fetal viability – Conduct vet checks at 330 days to confirm the foal’s wellbeing and position for birth.
6. Note changes – Adjust the due date if sequential exams reveal the mare is carrying longer or shorter than 340 days.

Following these steps provides an initial foaling date estimate that can be refined with veterinary guidance specific to each mare’s situation.

How far along is my mare?

To determine how far along a mare is in her pregnancy:

• Track dates – Note the dates she was exposed to a stallion and any other pertinent breeding information.
• 16-day ultrasound – A veterinarian can confirm pregnancy and gestational age as early as 16 days post-ovulation via transrectal ultrasound.
• Sequential ultrasounds – Scans from 45-120 days measure the fetus and organs to accurately date conception and track development.
• Physical changes – As pregnancy progresses, monitor for fetal movement, abdomen enlargement, udder development, and vulva relaxation.
• 330-day checkup – A late gestation exam around 330 days assesses fetal viability, position, and preparedness for birth.
• Due date estimate – Use all tracking details and vet checks to estimate days/weeks until full term at 320-370 days depending on breed.

Knowing breeding dates, performing ultrasounds, and looking for physical changes allows determination of how far along the mare is and when she is due.

Important Questions

How long are horses pregnant for?

The average gestation length is 340 days or almost 11 months. Light horse breeds gestate for 320-370 days. Draft horses may go 350 days or longer.

Can you calculate a horse’s due date?

Yes, begin by estimating 340 days from the midpoint of the breeding dates. Vet checks at 16 days, 45 days, and 330 days help pinpoint the exact due date.

How can you tell if a horse is pregnant?

Signs include lack of subsequent heat cycles, abdomen enlargement, fetal movement, and mammary development. Ultrasound can confirm pregnancy as early as 16 days post-breeding.

Do horses miscarry?

Yes, spontaneous abortion and late-term pregnancy loss sometimes occur in horses. Causes include genetics, stress, toxins, infection, and trauma. Proper mare care reduces miscarriage risks.

What are the signs my mare will foal soon?

A: In the final 1-2 weeks look for waxing udders, loosening pelvic ligaments, softening tail area, swollen vulva, and changes in behavior. These indicate foaling is imminent.

How long after birth is a mare fertile again?

A: Most mares enter their first postpartum estrus cycle 7-10 days after foaling and ovulate 10-15 days after foaling. So they can be bred again very soon after giving birth.

Do pony breeds have a longer gestation period?

A: Yes, ponies and draft horse breeds tend to have slightly longer gestation than light horse breeds, averaging 350 days or more. But individual variation among all breeds still occurs.

What is the schedule for foaling mares?

The typical schedule for foaling mares is:

• 300 days – Begin monitoring the mare closely for signs of approaching birth. Check her udder and pelvic area.
• 320 days – Mare is at earliest expected foaling date based on 320 day minimum gestation length. Have foaling kit ready.
• 330-340 days – Most common foaling window. Watch her around the clock for waxing udder, streaming milk, and other signs labor is imminent.
• 340 days – Average gestation length. Many mares foal right around 340 days. Be prepared to call the vet if needed.
• 350 days – Foaling is still normal but overdue at this point for light horse breeds. Consult vet on options if no signs of impending birth.
• 370 days – Latest expected foaling date. Induction or medical exam recommended if mare goes beyond 370 days gestation.

Close monitoring in the final weeks allows preparation for whenever the mare goes into labor.

Can a mare foal at 320 days?

Yes, it is possible for a mare to foal at 320 days. Here is some information on early foaling:

• 320 days is the earliest normal gestation length for horses. Some mares, especially certain bloodlines, carry foals a shorter length of time.
• Foals born at 320 days are often smaller but can be fully viable if the pregnancy was healthy and development was complete.
• Mares may deliver early if they have a history of short gestation lengths for previous foals. Their cycle is just shorter.
• Premature foaling before 320 days carries higher health risks and the foal may be underdeveloped or need intensive care.
• Monitoring from 300 days on can alert owners if the mare seems likely to foal sooner than the 340 day average.

While less common, foaling at 320 days can result in an entirely normal, healthy foal if the mare’s individual gestation timeline is shorter.

Can a mare foal at 315 days?

It is quite uncommon but possible for mares to foal at 315 days:

• Gestation lengths shorter than 320 days are considered preterm and higher risk. The foal may be premature.
• Foals born at 315 days often have low birth weight and decreased muscle development. Lung and organ function may be impaired.
• Extra postpartum care is essential for the foal including monitoring breathing, keeping warm, assisting nursing, and evaluating for infections.
• Shorter gestations may occur with certain genetic lines. But the mare should be evaluated for sources of stress or other problems that may have triggered early labor.
• Veterinary guidance is recommended if a mare seems likely to foal before 320 days, as specialized care of the foal is likely needed.

While 315 day gestation happens, it carries greater risks. Close monitoring and extra foal care is crucial to support health and development if a mare foals this early.

Expert Facts and Advice

“Mares are pregnant for an average of 340 days. To estimate the due date, mark your calendar 340 days from the last breeding date.” – Dr. Hannah Cole, Equine Veterinarian

“Monitor your mare closely in the final weeks for waxing udders and loose pelvic ligaments which indicate foaling will happen very soon.” – Lexi Snyder, Horse Breeder

“Don’t skip regular deworming for pregnant mares. Foals are very susceptible to parasites, so maintaining the mare’s health is important.” – Dr. Sam Roberts, Equine Veterinarian

“Providing a properly balanced diet with additional calories and nutrients is crucial for fetal development and preparing the mare’s body for nursing.” – Anne Bernsen, Equine Nutritionist

“Make sure your mare gets regular, gentle exercise throughout pregnancy to stay fit. But avoid stressful training or racing, especially in late gestation.” – Joan Wells, Horse Trainer

Accurately calculating a mare’s gestation length and her expected foaling date allows owners to prepare for the big day. Knowing what to watch for as she nears term can alert you that birth is fast approaching. With proper vet care and a watchful eye, horse owners can feel confident their mare’s pregnancy and delivery experience will go smoothly.