dairy cattle vs milker

dairy cattle and milker both are nouns.

Word	Noun	Adjective	Verb	Adverb
dairy cattle	Yes	No	No	No
milker	Yes	No	No	No

As nouns, dairy cattle and milker are synonyms defined as:

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

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