I don't see widespread use of animals in a city setting. Perhaps for the farmers bringing food in from the country. Mass transit, walking and bicycles make the most sense for short distance trips. But it is going to be a long hard transition.
I read an article a while back that was in an archive somewhere about the major issue of people abandoning dead horses on the streets of NYC and the cost to the taxpayers.
It was a sizable problem not to mention a public health nightmare. Then there was the issues of how to dispose of the carcasses. At one point IIRC they were dumping them in the Hudson River, but that was causing problems too, when they floated back in on the tide.
Aaron