pack animal

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An animal, such as a mule, used to carry loads.

from The Century Dictionary.

• noun A beast of burden used to carry packs, or to transport goods in bales, boxes, etc., on its back. See cut under pack-mule.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A domesticated animal used to carry heavy items.
• noun A wild animal that lives and hunts in packs

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun an animal (such as a mule or burro or horse) used to carry loads