In CivCraft normal animal breeding is disabled. The pasture is a 2x2 tile improvement which allows you to breed animals. Once you've researched Animal Husbandry you'll be able to breed animals at your pasture. Each time you breed an animal, the baby that is produced is counted towards that pasture's maximum animal count. When the pasture reaches its max, you will no longer be able to breed animals from that pasture until you kill some of them off.
The pasture remembers which animals were bred at which pastures, so taking them out of the pasture will NOT decrease the pasture's animal limit.
The animal limit for pastures is set to 30 animals per pasture. The type of animal does not matter. To get more animals than 30, you'll have to build more pasture improvements.
Like all Tile Improvements, pastures can be built anywhere inside your town's cultural borders. If they are built outside the borders of your town, it will be difficult to protect the animals that are being kept inside since anyone will be able to build or dig their way into the pasture.