The most common and most likely answer to this crossword clue is the 5 letter word SWILL
I've seen this crossword clue in Financial Times
S
W
I
L
L
More clues leading to the result SWILL
- Son is going to drink a lot
- Piglet’s grandfather – 8 this – probably ate this
- Refuse second preference
- Son has desire for animal food
- Westminster district Liberals drink heavily
- Determination comes after second drink
- Southern inclination to drink greedily
- Son is going to drink
- Leave after second large drink
- In short piece, Shakespeare’s found a depository for hogwash
Buddy explains!

The straight part
We know that "animal food" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case animal food = swill.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 SWILL mean?
SWILL noun- (collective) A mixture of solid and liquid food scraps fed to pigs etc; especially kitchen waste for this purpose.
- (by extension) Any disgusting or distasteful liquid.
- (by extension) Anything disgusting or worthless.
- A large quantity of liquid drunk at one swallow.
- Inexpensive beer or alcohol.
- (Ultimate Frisbee) A badly-thrown pass.
- To drink (or, rarely, eat) greedily or to excess.
- To wash (something) by flooding with water.
- To move (a liquid or liquid-filled vessel) in a circular motion.
- (of a liquid) To move around or over a surface.
- To inebriate; to fill with drink.
- To feed swill to (pigs).