It would be a zoo. If you are writing (or saying) a word that begins with a Vowel, (A,E,I,O,U and sometimes Y) than you would put an AN at the beginning of the word. If the word began with a...
Very few zoos actually take animals from the wild these days. The majority of zoos will either trade, lend, or give a captively bred (meaning their parents were bred and gave birth to them in a zoo)...
Most don't really mind but some get frustrated. Additional Info: Most modern zoos are making great strides, or making an effort to meet the needs of their animals by supplying them with "enrichment...