Raw material used in pig production (4,3)
I believe the answer is:
iron ore
This clue might be a double definition.
'raw material' is the first definition.
'iron ore' can be an answer for 'material' (iron ore is a kind of material). I'm unsure of the 'raw' bit.
'pig production' is the second definition.
Although both the answer and definition are singular nouns, I don't understand how one could define the other.
'used in' acts as a link.
Can you help me to learn more?
(Other definitions for iron ore that I've seen before include "Nero or I (anag) -- from which a common metal comes" , "Metal-bearing mineral" , "Material containing ferric metal" , "Useful mineral" , "Haematite, for example -- Nero or I (anag)" .)