Are white ones visibly foaming? (6)
I believe the answer is:
horses
If this is the answer, I'm afraid I cannot explain it.
Can you help me to learn more?
(Other definitions for horses that I've seen before include "Equine beasts" , "Hoofed mammals (which go with 19 4)" , "Equines" , "Domesticated animals" , "Equine animals" .)