To make animals visible again go to File > Select Society (or press F7 on your keyboard). A list of available societies will become available. Select the society you believe your animals are located in. You will be prompted that a society change has been done. See below images:
If you still cannot locate your animals after the society change has been completed, you may still be in the incorrect breed society. You can check that the animals are in your Stockbook by going to the All Societies option. See below image: