Crossword Genius

Horses incapable of continuing race? (8)

Ross

I believe the answer is:

geldings

I'm a little stuck... Click here to teach me more about this clue!

'horses' is the definition.
The definition and answer can be both animals as well as being plural nouns.
Maybe you can see an association between them that I can't see?

I don't understand how the remainder of the clue works.

Can you help me to learn more?

I've seen this clue in The Telegraph.
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