The Collaborative International Dictionary of English v.0.48:

Foremilk \Fore"milk`\, n. (Physiol.)
   The milk secreted just before, or directly after, the birth
   of a child or of the young of an animal; colostrum.
   [1913 Webster]

WordNet (r) 3.0 (2006):

foremilk
    n 1: milky fluid secreted for the first day or two after
         parturition [syn: colostrum, foremilk]