One thing to note is most zoos, wildlife parks, and captive habitats have copyrights on their animals and strictly prohibit commercial photography without their permission.
I photograph at both zoos and in "the wild" and I use them for different reasons. My zoo shots are just for playing around - to get used to equipment and to practice in a controlled environment. In the wild I will typically have very little time to react, so it is very wise to be familiar with my equipment ahead of time.
Getting photographs in the wild is difficult, but it's also very rewarding. I am not a full time wildlife photographer, but I do spend at least an hour a day on it. Many days I only "get" a few ducks or sparrows, but once in awhile I get something very nice. Last week (while on my first walk with my 7D2) I found a coyote. Over the weekend I found a family of river otters.
Animals are very different when in their own element vs. when they depend on people for food and care. There is a different look to the animal's eyes.
Also keep in mind that a number of famous photographers have had their reputations ruined because they passed off a wild animal park photo as a truly wild one.
The ranches and parks we are talking about are pay per use places... They know you are using them for commercial use... They typically have more authentic enclosures so they look good photographically...