A female horse is called a mare when she is an adult, usually 4 years old and older.

Quick Scoop

  • A young female horse (typically under 4 years old) is called a filly.
  • An adult female horse is called a mare.
  • A female used for breeding is often simply called a broodmare.

So if you’re talking about a grown “girl horse,” the word you’re looking for is mare.

In horse terminology, “mare” is to horses what “cow” is to cattle: the standard word for an adult female.

TL;DR:

  • Young female = filly
  • Adult female = mare
  • Breeding adult female = broodmare

Information gathered from public forums or data available on the internet and portrayed here.