it depends on the context, you could try "labourer" or use whatever the local "workhorse" is.
Onus
animal, beast, brute, critter, varmint
The plural of beast is beasts.
A burden is unwanted. Yes, the word has negative connotations.
The noun 'burden' is an abstract noun as a word for something hard to bear; something oppressive or worrisome; a word for a concept.The noun 'burden' is a concrete noun as a word for a load that is carried; a word for a physical thing.
donkey
In the Andes the main beast of burden is the llama.
A beast of burden used in the North African desert is a camel.
The beast of burden to Native Americans were dogs.
beast of burden
A donkey carries goods in panniers, it is a beast of burden. The lead singer of the pop group the Animals was Eric Burden. (No extra charge for 2)
Llamas and alpacas are the common beast of burden to Peru and Chile
Beast.
Llama
Llamas
camel
Camel