The most common and most likely answer to this crossword clue is the 4 plus 8 letter word JOHN DOLITTLE
I've seen this crossword clue in Financial Times
J
O
H
N
D
O
L
I
T
T
L
E
Buddy explains!
The straight part
We know that "Animal-loving docto" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case animal-loving docto = john dolittle.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.