The gestation of a horse is significantly longer than the gestation of humans. Ranging from 320 to 380 days, the average gestation length falls between 330 to 345 days.
A horse embryo can be seen by ultrasound as early as 12 to 14 days after conception. Between days 15 and 17, the embryonic vesicle becomes more fixed to the wall of the uterus, and the embryo is easier to visualize.
The heartbeat is detectable on ultrasound imaging to verify the presence of a viable fetus between days 24 and 28.
Check out our recent posts below throughout the season to learn more about reproductive health and breeding methods, and select “Read More” below to see all our Breeding/Reproduction blog posts.

The Pregnancy Wheel, developed by the University of Guelph, is a great online resource with information covering a mare's pregnancy through all three trimesters and the foaling window.

Cutomizable to a mare's breeding date, the Pregnancy Wheel provides an overview of fetus growth and milestones during each month, and it offers considerations on risk factors and mare management during each trimester.  

Education Blogs

Gestation length varies widely in mares. Although there is no foolproof method for predicting foaling, there are some commonly observed signs. In this article available on The Horse, Heather Smith Thomas provides a solid overview of some signs of foaling, including increased udder size, waxing (dried secretions on the tips of the teats), and the softening of pelvic ligaments around the tailhead. Thomas also details possible behavioral changes, including increased restlessness, pacing, and tail swishing and lifting. 

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In this video from Foal Patrol Season 3, Dr. Tanner from Rood and Riddle discusses featured mare Magical World's 61 day post-ovulation ultrasound, including fetal gender determination.

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