Ringling has never bred "on tour" in the last 20 years. The breeding bulls are all in the Florida breeding/retirement center. The only bulls they had on tour in the last decade were the bull calves, at least until he was about 7 years old when he "vanished" from the shows. And the very big, castrated male from Patrizia Zerbini "Luke" who is not owned by Ringling has performed in the "Gold tour". I am 100% sure that they never had any mothers with the calves on tour in the last decade - like the bulls, the mothers stay at the breeding facility. The calves that are chosen for travelling are usually weaned when they are 1,5-2 years old and then taken on tour at age 2. This is what happened with the calves born in 2002 and before. You must have seen pictures of the calves with other females and being lied to, or pics older then 15 years. I have not heard anything about the youngest calves born from 2005 on travelling, so maybe they are still with their mothers.
Certainly not all animals in zoos are kept in ideal social groupings, but at least it is possible to build enclosures suitable for good social groups, while it is totally impossible for a circus to travel with a breeding bull elephant, or a breeding group of rhinos, hippos or giraffes.
By the way, circus Krone is the worst possible example for good elephant husbandry you could have picked - I have seen that circus a number of times in the last years and I can tell you that these elephants usually never see a forest nor a river. They hardly ever leave their tent!! Circus Krone is the largest circus in Germany and they never have much space for outdoor enclosures, all their tents and trucks hardly fit on an average circus place. And their elephants don`t come along and have to be kept seperate in 3 or even 4 groups (that changes), while they never have more then 2 outdoor paddocks. These paddocks are hardly ever used, because some elephants have learned to climb out and the trainer needs to keep an eye on them all the time when they are outside. Seems he doesn`t have the time to do that more then two- three hours in the moring IN THE BEST CASE. The rest of time, the eles are chained in their tent. I have never seen such bad swaying like in the Krone circus elephants. And most of their elephants have some sort of foot problems.. no wonder, they hardly ever get to walk on grass or sand. Krone is hell for elephants, I have seen a number of smaller circusses doing much better. The paddocks may be small and have concrete floor and no pool nor mud, but at least there are a number of smaller circusses whose elephants are outside all day (before being chained for the night in the tent...).
@ dragon: You`re correct that activity is the goal of enrichment, but not all "activity" is positive. In animals, enrichment shall encourage natural behavoir (and though this, enhance the wellbeing of the animal through stimulating body and mind). A child that is forced to work 12 hours each day in a mine certainly has a very active life, but not in a way that would be beneficial to body and soul.
Yet I very much doubt that even with performing, circus animals are more active then zoo animals in a good environment - circus enclosures are usually only a fraction of good zoo enclosures in size, and without any vegetation and euqippment, animals have no reason to move.