A long time mostly producing fodder (6)
I believe the answer is:
forage
'fodder' is the definition.
(thesaurus)
'a long time mostly' is the wordplay.
'a long time' becomes 'forages' ('for ages' can mean for a long time).
'mostly' means to remove the last letter.
'forages' with its final letter taken off is 'FORAGE'.
'producing' is the link.
(Other definitions for forage that I've seen before include "Search around for food" , "Hunt for food or provisions" , "Rummage, search for" , "Plunder; rummage" , "Collect food" .)