The most common and most likely answer to this crossword clue is the 6 letter word MUTTON
I've seen this crossword clue in The Sunday Telegraph
M
U
T
T
O
N
More clues leading to the result MUTTON
Buddy explains!

The straight part
We know that "sheep" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case sheep = mutton.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.
What does MUTTON mean?
MUTTON noun- The flesh of sheep used as food.
- The flesh of goat used as food.
- A sheep.
- Em, a unit of measurement equal to the height of the type in use.
- A prostitute.
- An old Anglo-French gold coin impressed with the image of a lamb.
- Deaf.