The most common and most likely answer to this crossword clue is the 7 letter word HEADAGE
H
E
A
D
A
G
E
Buddy explains!

The straight part
We know that "Payment per animal" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case payment per animal = headage.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 HEADAGE mean?
HEADAGE noun- The number of stock animals (head) on a farm.