I re-read the AZA accreditation standards after I realized that I may have misinterpreted some parts of them the first time. One thing that was interesting is the AZA standards for visitor interactions with various animals. It's apparently allowable for visitors to interact with reptiles, primates and hoofstock if the specimens are extensively tested for disease. Since primates need to be tested for a lot of things and salmonella cannot be eradicated in reptile populations (forcing zoos to enforce hand-washing), I understand why zoos would be disinclined to bother with the precautions they need to allow visitor interactions. However AZA zoos allow giraffe feeding and sometimes domesticated hoofstock in petting zoos, and concerns seem to be similar for a domestic pig vs a peccary or a domestic goat vs a duiker. I've also noticed that non-AZA zoos with hoofstock usually seem to let their visitors feed them (and in a few cases even pet them). So I guess what I'm wondering is A. why AZA zoos seem not to allow feeding of animals other than giraffes, and B. why I've never small hoofstock in walk-in exhibits at AZA zoos? With large hoofstock I get that there's a concern for visitors literally getting their toes stepped on, it occurred to me that if I were to design a large aviary I'd want to include some animals other than birds (despite my love of birds) if the wouldn't cause problems for other occupants (like I imagine peccaries would eat eggs of ground-nesting birds). So duikers in an Africa aviary or chevrotains in an Asia aviary seem like good candidates for that. And I'm wondering if there's a reason I haven't seen a zoo do it?
There have been examples (and probably many) of smaller hoofstock in walk-in aviaries. Off the top of my head, I can think of the old tropical aviary at the erstwhile Bird House at the Cleveland Zoo (which had suni at Kirk's dik-dik over the years, nearly always one of the two) and for a current example, the pheasant aviary at the Columbus Zoo (which holds the zoo's elderly Reeves' muntjac that formerly shared an exhibit with the white-naped crane). In Cleveland, the walkway through the aviary was not at ground level, so there was no chance of interaction between the dik-dik/suni and visitors, but at Columbus, one can get very near the muntjac (although there are always docents present, so I think touching is probably highly discouraged if not forbidden). I'm sure there are more examples out there - I'm fairly certain I've seen chevrotains in walk-through aviaries as well but I can't recall specifics. As to feeding, besides giraffes, I know of some AZA institutions that do allow (or have allowed) the feeding of rhinos (usually in limited situations, such as behind the scenes tours or special events) - I myself have a great picture of me feeding and touching a large Indian rhino at the Wilds somewhere. The petting kraal at the San Diego Safari Park used to hold a lot of habituated hoofstock, many younger individuals, but some adults as well. I wouldn't be surprised if deer feeding was allowed at some AZA institution (many years ago, Sea World of Ohio had a deer feeding/petting park).
Kansas City Zoo has (or at least had) Dik-dik in their walk-through African aviary. I only saw it out in the open once, though. There is also an area where the feeding/petting of fallow deer is permitted through a fence. Many larger species (as mentioned by jibster) permit contact in behind the scenes tours and similar situations. I was allowed to pet and feed Indian rhino at the San Diego Zoo Safari Park. I pet common hippos at the LA Zoo. The San Diego Zoo had an "Inside Look- Surprise" tour where you get shuttled around the zoo and go to the behind-the-scenes areas of two random species. I got giraffes, which I normally wouldn't be too wild about, except I got a good glance at the twelve day old (at the time) baby. Another option is okapi- the same deal (feeding/petting through fence), but a much cooler species. I've seen various zoos with interaction programs with white rhinos, in addition to the aforementioned greater one horned rhino.
I think the obvious reason for not allowing it in general is so that visitors will not get bitten. Giraffes are safe because they use their very long tongues to get the food so their teeth never come near a visitors hand. With male antelope (and females of some species such as oryx) the horns pose an obvious danger as well. As mentioned some places do rhinos as part of a special tour. My local zoo regularly does special visits with white rhino which seem to be quite docile (though visitor bodies are still separated by thick posts from the rhino body).
Some European examples: - At the Maubeuge Zoo (France) I've been in a large walk-through enclosure with guanacos. They are not shy at all. It is very easy to pet them. - The Domaine des Grottes de Han (Belgium), has a huge enclosure with przewalski's horses, Heck cattle, red deer, fallow deer and moufflon. You can walk through the edges of the exhibit, although I have never seen an animal coming really close to the path. Before the przewalski's horses moved to this exhibit, it held tarpan horses. - Inside the Africa Dôme of Randers Regnskov (Denmark) there are free-ranging blue duikers.
I'd say that fallow deer walk-throughs are practically a staple in European wildlife parks that specialize in native species. More European (Danish) examples: Ree Park's pampas exhibit with Patagonian cavies, vicunas and rheas is walk-through, and Jyllands Park Zoo has a walk-through sika deer exhibit. When Randers Regnskov kept chevrotains, they were sometimes free-ranging in the Asia Dome and sometimes kept in an enclosure.
Among my nicest memories from zoos are feeding ungulates through the fence. Wisent, ibex, red deer, maned sheep, fallow deer etc. In small native parks or enclosures where it is allowed. I think this is untaped potential for zoos to easily make popular exhibits. Among things free-ranging not yet mentioned I saw wild boar (small park near Zurich), ibex (Switzerland somewhere), blackbuck (Beekse Bergen) and chevrotain (several tropical halls). In all cases it were big natural areas, and ungulates were not tame. So they kept away and it did not matter if there was a barrier between visitors or not. But I would not mix the two, that is letting adult ungulates wander among people is dangerous.
