milker vs milch cow

milker and milch cow both are nouns.

Word	Noun	Adjective	Verb	Adverb
milker	Yes	No	No	No
milch cow	Yes	No	No	No

As nouns, milker and milch cow are synonyms defined as:

Other synonyms of milker include dairy cattle, dairy cow, milcher, milk cow.

milker (noun)	milch cow (noun)
cattle that are reared for their milk	cattle that are reared for their milk