Chicken crossing bridge with one dog (6,7)
I believe the answer is:
cocker spaniel
'dog' is the definition.
(cocker spaniel is a kind of dog)
'chicken crossing bridge with one' is the wordplay.
'chicken' becomes 'cockerel' (cockerel is a kind of chicken).
'crossing' is an insertion indicator (to cross can mean to go over or around).
'bridge' becomes 'span' (synonyms).
'with' says to put letters next to each other.
'one' becomes 'i' (Roman numeral).
'span'+'i'='spani'
'cockerel' placed around 'spani' is 'COCKER SPANIEL'.
(Other definitions for cocker spaniel that I've seen before include "Ponies crackle (anag) - dog" , "Small dog used in game shooting" , "Breed of gun dog" , "Mutt" , "Breed of small dog" .)