Head of farm gets more unusual feed (6)
I believe the answer is:
fodder
'feed' is the definition.
(fodder is a kind of feed)
'head of farm gets more unusual' is the wordplay.
'head of' says to take the initial letters.
'gets' means one lot of letters go next to another.
'more unusual' becomes 'odder' ('odd' can be similar in meaning to 'unusual'**).
The initial letter of 'farm' is 'f'.
'f'+'odder'='FODDER'
(Other definitions for fodder that I've seen before include "Food for livestock" , "Straw to eat" , "Bulk feed for livestock" , "Animal feed" , "Lucerne etc" .)