Company at sea drink a nutritious substance (9)

I believe the answer is:

colostrum

'a nutritious substance' is the definition.
(type of milk produced by mammals after birth)

'company at sea drink' is the wordplay.
'company' becomes 'co' (abbreviation).
'at sea' becomes 'lost' (I've seen this before).
'drink' becomes 'rum' (rum is a kind of drink).
'co'+'lost'+'rum'='COLOSTRUM'

I've seen this clue in The Times.

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