The Collaborative International Dictionary of English v.0.48:

Milker \Milk"er\, n.
   1. One who milks; also, a mechanical apparatus for milking
      cows.
      [1913 Webster]

   2. A cow or other animal that gives milk.
      [1913 Webster]

WordNet (r) 3.0 (2006):

milker
    n 1: cattle that are reared for their milk [syn: dairy cattle,
         dairy cow, milch cow, milk cow, milcher, milker]

Moby Thesaurus II by Grady Ward, 1.0:

42 Moby Thesaurus words for "milker":
   Brahman, Indian buffalo, aurochs, beef, beef cattle, beeves, bison,
   bossy, bovine, bovine animal, buffalo, bull, bullock, calf,
   carabao, cattle, cow, critter, dairy cattle, dairy cow, dogie,
   heifer, hornless cow, kine, leppy, maverick, milch cow, milcher,
   milk cow, muley cow, muley head, musk-ox, neat, ox, oxen, steer,
   stirk, stot, wisent, yak, yearling, zebu