The most common and most likely answer to this crossword clue is the 6 plus 6 letter word GORDON SETTER
I've seen this crossword clue in The Times
G
O
R
D
O
N
S
E
T
T
E
R
More clues leading to the result GORDON SETTER
Buddy explains!

The straight part
We know that "Breed" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case breed = gordon setter.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.