The Messenger of Allah (ﷺ) used to name a mare a horse.
Sunan Abi Dawud Book 15, Hadith 70
← Previous Hadith The Prophet (ﷺ) said: The most favoured horses are the sorrel.

Sunan Abi Dawud Book 15, Hadith 69 Next Hadith → Abu Hurairah said “The Prophet (ﷺ) disapproved the shikal horses. Shikal are the horses that are white on their right hind leg and white on their left foreleg or white on their right foreleg and left hind leg.

Abu Dawud said “This means alternate legs”.

Sunan Abi Dawud Book 15, Hadith 71