General terms:
* Draft animal: This is a broad term for any animal used for pulling loads.
* Work animal: This term is also broad and encompasses animals used for various tasks, including pulling, carrying, and herding.
* Pack animal: This refers to an animal used for carrying loads on its back.
* Hauling animal: This emphasizes the animal's role in transporting goods.
More specific terms:
* Pack horse: For horses specifically used for carrying loads.
* Mule: For a hybrid animal used for carrying loads.
* Ox: For cattle used for pulling loads.
* Donkey: For donkeys used for carrying loads.
* Camel: For camels used for carrying loads in desert regions.
Figurative terms:
* Toil-slave: This term emphasizes the hard work and lack of choice the animal has.
* Workhorse: This term can be used metaphorically to describe a person who works hard.
The best word to use depends on the specific situation and the desired effect.