I recently went to a "traveling zoo" type of thing, and the conditions the animals were in were horrifying. I decided to do some research, and the zoo met the APHIS USDA guidelines. The guidelines say that a cage only has to be as big as the animal's movements based on the species (how it lays or stands). The USDA also encourages tattoos or tags for animals you've boughten. 
I believe animals deserve to live in a space large enough for them to roam freely. These animals are living things that deserve the best life they can possibly have; they are not here simply for our entertainment or enjoyment.