pack animal vs beast of burden

pack animal and beast of burden both are nouns.

Word	Noun	Adjective	Verb	Adverb
pack animal	Yes	No	No	No
beast of burden	Yes	No	No	No

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

pack animal: an animal (such as a mule or burro or horse) used to carry loads
beast of burden: an animal such as a donkey or ox or elephant used for transporting loads or doing other heavy work

Other hypernyms of pack animal include jument.

pack animal (noun)	beast of burden (noun)
an animal (such as a mule or burro or horse) used to carry loads	an animal such as a donkey or ox or elephant used for transporting loads or doing other heavy work