dairy cattle vs milk cow

dairy cattle and milk cow both are nouns.

Word	Noun	Adjective	Verb	Adverb
dairy cattle	Yes	No	No	No
milk cow	Yes	No	No	No

As nouns, dairy cattle and milk cow are synonyms defined as:

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

dairy cattle (noun)	milk cow (noun)
cattle that are reared for their milk	cattle that are reared for their milk