work animal vs beast

work animal and beast both are nouns.

Word	Noun	Adjective	Verb	Adverb
work animal	Yes	No	No	No
beast	Yes	No	No	No

As nouns, beast is a hypernym of work animal; that is, beast is a word with a broader meaning than work animal:

Other hypernyms of work animal include animal, animate being, brute, creature, fauna.

work animal (noun)	beast (noun)
an animal trained for and used for heavy labor	a living organism characterized by voluntary movement
	a cruelly rapacious person