Charge by the day for fodder (4)
I believe the answer is:
feed
'fodder' is the definition.
(I've seen this before)
'charge by the day' is the wordplay.
'charge' becomes 'fee' (fee is a kind of charge).
'by' is a charade indicator (letters next to each other).
'the day' becomes 'd' (abbreviation for day).
'fee'+'d'='FEED'
'for' is the link.
(Other definitions for feed that I've seen before include "Give food to; eat" , "Give (or take) nourishment" , "comedian's assistant" , "Straight man" , "Take food" .)