Question: what is the idiomatic expression of horse?
Answer: as strong as a horse/ox. - very strong. ... 
as stubborn as a mule. - very stubborn. ... 
back the wrong horse. - to support someone or something that cannot or does not win or succeed. ... 
beat a dead horse. ... 
bet on the wrong horse. ... 
by shank's mare. ... 
champ/chomp at the bit. ... 
change horses in midstream.