We did it this morning and saw everything, didn't do the train ride as that was extra and we even saw the pig races and we were done in an hour and a half. If you have kids I would recommend bringing some quarters for feeding machines and some money to buy carrots.
A few hours they had new exhibits that were under construction when we were there.
If you want to really enjoy the place I would set aside 2-3 hours to go through the whole place. Also when you are purchasing the tickets take into consideration that you will probably need $14 for food for the animals
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