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When Do Mares First Go Into Heat?

Name: Ask the Vet - When do mares first go into heat?
Uploaded: 2020-01-03T00:00-05:00
Description: In this Ask the Vet video, Dr. Gray and SmartPaker Dan discuss the estrous cycle in fillies and mares. Dr. Gray lists the signs that your mare is in heat, shares how old fillies typically are when they first come in season, and advises at what age you should probably start separating the fillies from the colts.

Updated September 22, 2025

In this Ask the Vet video, Dr. Lydia Gray and SmartPaker Dan discuss the estrous cycle in fillies and mares. Dr. Gray lists the signs that your mare is in heat, shares how old fillies typically are when they first come in season, and advises at what age you should probably start separating the fillies from the colts.

Additional Mare Owner Resources

Understand what "mareish behavior" means.
Watch this video for help on reducing pain for a mare in heat.
Learn what you can expect when using supplements for mares.

SmartPak Equine, LLC strongly encourages you to consult your veterinarian regarding specific questions about your horse's health. This information is not intended to diagnose or treat any disease, and is purely educational.