pack animal 
noun
1An animal used to carry loads.They traveled on the jungle trails until they had to abandon the pack animals and continue on foot, carrying their supplies on their backs....
- Prior to the arrival of the railroad, all freighting was done by wagon or pack animal.
- He pushed open the gate of the donkey's stall, and led the pack animal into the main row of the stables.
2An animal that lives and hunts in a pack.Dogs are pack animals and den animals, and very much creatures of habit....
- All pack animals have a lead animal, in the case of dogs it is the alpha dog.
- Oliver is a dog and dogs - being pack animals - are capable of forming relationships with humans premised upon a reciprocity of affection.