Start breeding birds and dogs (7)
I believe the answer is:
beagles
'dogs' is the definition.
(beagle is a kind of dog)
'start breeding birds' is the wordplay.
'start breeding' becomes 'b' (I can't explain this - if you can you should believe this answer much more).
'birds' becomes 'eagles' (eagle is a kind of bird).
'b'+'eagles'='BEAGLES'
'and' acts as a link.
Can you help me to learn more?
(Other definitions for beagles that I've seen before include "Short-legged hounds" , "Dogs" , "These hounds bag eels badly" , "Hunting hounds" .)