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Foaling Calculator

I Am Ranch Miniature Horses is sharing with you what we do to maintain the health of our horses. This is not intended to direct you on how to care for your horse. The intent of this is only to share what we do, and raise questions for you. We advise you to consult your veterinarian before making any changes in your horse's health care. The information found on our website is not to supersede the advise of your veterinarian. I AM Ranch Miniature Horses cannot be held liable for the care of your horse(s).

Use these calculators to check your Mares Foaling Date: Equine Foaling Estimator

Calculate mare's approximate due date
Enter last breeding date in format

Desired gestation duration:
You can change the above number!

Estimated foaling date:
Number of days mare in foal
Enter last date mare was bred:

Enter today's date:

Estimate of days
mare is in foal


Here are some quick facts: Most mares cycle every 21 days. The egg is viable for 24 hours and semen is viable for 48 hours. If there is a low sperm count, it is a good idea to breed daily. Allowing the mare and stallion to pasture breed gives you the best chance for a foal.
Gestation averages about 336 days. For a due date count back 25 days. If she was last bred on April 26, she's due on April 1. This could vary by 20 days early or late. Supposedly, research has shown that 70% of all mares may repeat their first pregnancy cycle regardless of whether it is a filly or colt. If you know the number of days of her gestation in previous pregnancies, you can check that number against this pregnancy to see how close she is to repeating her cycle each year.  Keeping a record of each mare's pregnancies is thus helpful.

You really  need to be present when your mare has her baby. I believe you owe this to her. So many babies don't make it because the owners were not present. They get stuck (dystocia) or suffocate in an unbroken sac. Many miniatures go early, so after day 300, we try to watch our mares very closely. Having cameras on her stall really aid in the monitoring process, as does milk strip testing. Click here to buy foal time strips

The mare's eggs can "float" for up to 2 weeks before it implants in the uterine lining. Thus there is a larger window of gestation for horses.  We did have a fun thread on our AZminiatures yahoo group wherein one breeder told of a mare that went 384 days and another mare who waited 372 days. Those have got to be record long for gestation times. On the short end, one miniature breeder told of a baby born at 296 days with only peach fuzz, no hair and cartilage for legs. The vet told this lady she would die, but love and determination (along with lots of hours) has grown this baby up to be 4 years old now. They had to be there every 2 hours around the clock and support her while she nursed. After 2 weeks, she was getting up on her own! As you can see, there can be a great amount of variation.

There are urine tests you can buy to preg check your mare. Checking can also be done via a blood test or ultrasound.

We narrow down our foaling dates by looking at all the signs of foaling and by using milk strips!

I have been told by a few different vets that mares due in the early part of the year or in colder climate, birth later than average, and that those mares due in the early spring or in warmer climates are more likely to birth on time or a bit earlier than average. Could this be because the foals born in colder climates and earlier in the year need to grow a longer coat of fuzz before they pop out?

Foal heat is normally 10 days post foaling. Again there is a lot of variance. Our favorite mare comes in 18 days post foaling.

Is your mare overdue? Click here for a great article that will give you some parameters.

Diestrus = The time period a mare is not in heat. This time frame is more universal and is averages about 14 days. This time is when the mare is refusing the stallion.

Estrous = describes the entire reproductive cycle. Approximately 21 days.

Estrus = the time period wherein a mare is receptive to the stallion. This supposedly lasts for 5-7 days, and ovulation occurs in the last 24-48 hours of this time period. That is why we use the last breeding date as the one to calculate gestation from.

Anestrous = absences of estrus.

Need more reading??

Data Collection Chart is available to chart your mare's progression

Click here for a foaling calculator

Click here for a foaling kit list

Click here for ideas of  what to do 30 days prior to foaling

Click here for a description of a redbag birth

Click here for notes about dystocia during foaling

Read product testimonials here

Click here for our post foaling check list

Click here for instructions on how to use Foal-Time Strips

We have kept extensive foaling journals to help others.....Find them on the articles page




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