The most common and most likely answer to this crossword clue is the 5 letter word PINTO
P
I
N
T
O
Buddy explains!
The straight part
We know that "horse" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case horse = pinto.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does PINTO mean?
PINTO noun- A horse with a patchy coloration that includes white.
- Pied, mottled.